I. Introduction 

– Brief background on blockchain technology and its growth over the past decade

– Overview of the most popular blockchain platforms and languages used for development today

II. Ethereum

– Overview of Ethereum as a leading smart contract blockchain platform

– Introduction to Solidity as the main programming language for Ethereum dApps

– Explanation of key features of Solidity like contracts, functions, data types, etc.

– Examples of popular dApps built on Ethereum like CryptoKitties, Decentraland, etc.

– Resources for learning Solidity and building on Ethereum

III. Hyperledger Fabric

– Overview of Hyperledger Fabric as a private/permissioned blockchain framework 

– Introduction to chaincode programming using Go language 

– Explanation of chaincode functions, endorsements, channels, etc.

– Discussion of Hyperledger Fabric’s modular architecture and scalability

– Examples of enterprise blockchain solutions using Hyperledger Fabric

– Resources for learning Hyperledger Fabric and chaincode development

IV. Cardano

– Background on Cardano as a 3rd generation proof-of-stake blockchain

– Overview of Plutus as the smart contract language for Cardano 

– Explanation of Plutus features like validators, scripts, functions, etc.

– Examples of DeFi apps and use cases being built on Cardano

– Resources for learning Plutus and developing on Cardano

V. Polkadot

– Introduction to Polkadot and its multi-chain interoperability 

– Overview of Substrate framework and Ink! for developing parachains

– Explanation of Ink!’s syntax, macros, storage items, events, etc.

– Examples of parachains connected to Polkadot like Acala, Moonbeam, etc.

– Resources for learning Substrate and Ink! for Polkadot development

VI. Cosmos

– Background on Cosmos SDK for building application-specific blockchains

– Introduction to Go as the main language for Cosmos SDK development 

– Explanation of modules, transactions, governance, IBC protocol, etc. 

– Examples of Tendermint-based blockchains built with Cosmos SDK

– Resources for learning Go and Cosmos SDK for blockchain development

VII. Conclusion

– Summary of key platforms and languages covered

– Discussion of blockchain interoperability and future directions 

– Final thoughts on selecting the right platform and language for your needs

Introduction

Over the past decade, blockchain technology has grown from a niche concept into one of the most talked about and disruptive innovations of our time. An increasing number of companies, developers, and enthusiasts are exploring ways to harness the potential of blockchains across industries. This rapid growth has led to a diverse ecosystem of blockchain platforms, each with their own unique capabilities, consensus models, and programming languages.

In this comprehensive guide, we take a deep dive into some of the most popular blockchain platforms and programming languages used for development today. Whether you are looking to build a public, open-source blockchain network or an enterprise-grade private ledger, understanding the key options available is crucial for selecting the right framework for your needs. 

Ethereum

Ethereum stands out as the most widely used public blockchain network for decentralized applications (dApps). Launched in 2015, Ethereum extends the blockchain concept beyond just payments and introduces smart contract functionality. 

Smart contracts are executable programs that run on the Ethereum virtual machine (EVM). They allow developers to encode complex business logic and build decentralized apps (dApps) that inherit the reliability and security of the underlying blockchain.

Solidity is the main programming language used to write Ethereum smart contracts. It is a contract-oriented language inspired by JavaScript, Python, and C++. Some key features of Solidity include:

– Contracts – The building blocks of Solidity programs. They contain state variables, functions, modifiers, structs, etc.

– Functions – Used to execute specific tasks and modify state variables in a contract.

– Data types – Integer, boolean, address, bytes, string etc. for declaring variables.

– Inheritance – Contracts can inherit properties and methods from other contracts.

– Events and structs – For organizing data and emitting log events. 

Thanks to Solidity’s accessibility and Ethereum’s first-mover advantage, hundreds of dApps have already been built, ranging from games to DeFi protocols. Popular examples include:

– CryptoKitties – A blockchain-based virtual game that allows breeding and trading unique digital cats.

– Decentraland – A virtual reality universe powered by Ethereum, where users can create avatars, buildings, and applications. 

– Uniswap – A decentralized exchange for trading Ethereum-based tokens without intermediaries.

For those looking to learn Solidity, there are many online courses and tutorials available. The official documentation at solidity.readthedocs.io is a great resource to understand language features. Remix IDE provides an in-browser IDE for testing smart contracts. Overall, Ethereum remains the most active hub for public blockchain dApp development today.

Hyperledger Fabric 

While Ethereum leads for public blockchain networks, Hyperledger Fabric emerged as one of the most widely used frameworks for private and consortium blockchains. Originally contributed by IBM and Digital Asset, Fabric offers a modular architecture that enterprises can customize for their specific needs.

Smart contracts in Fabric are written as chaincode programs using general-purpose programming languages like Go, Java, JavaScript, etc. Go is the most common choice as it provides good support for cryptography, concurrency, and interfaces required for chaincode.

Some key Hyperledger Fabric concepts include:

– Permissioned network – Participants are known and authorized to transact. 

– Channels – Allow subgroups of network members to create separate ledgers while sharing some common infrastructure.

– Chaincode functions – Init, Invoke, Query methods for chaincode-to-ledger interactions.

– Endorsement policies – Rules for which peers must validate chaincode transactions.

– Consensus – Supported consensus algorithms include SOLO and Kafka. 

Hyperledger Fabric delivers scalability, resiliency, flexibility and privacy – making it attractive for enterprise use cases. Many companies use Fabric to streamline operations and create transparency across departments. Example use cases include:

– Supply chain tracking – Monitoring movement of goods across locations and checkpoints.

– Loyalty programs – Recording points earned and used by members in a transparent ledger.

– Trade finance – Digitizing records like letters of credit between exporters, importers and banks.

For those looking to learn Hyperledger Fabric, the official documentation at hyperledger-fabric.readthedocs.io is a good starting point. There are also training resources offered by The Linux Foundation and third-party providers. Overall, Fabric’s modular approach makes it well-suited for a wide variety of enterprise blockchain applications.

Cardano

Beyond Ethereum and Hyperledger, Cardano stands out as another actively developed open-source blockchain platform. Created by IOHK and led by Charles Hoskinson, Cardano aims to deliver a “3rd generation” blockchain with improved security, governance, and scalability. 

The Cardano blockchain uses a proof-of-stake consensus model called Ouroboros, which determines block producers through coin ownership rather than mining power. Cardano also utilizes layered architecture, separating the settlement layer from the control layer.  

The native smart contract language for Cardano is called Plutus – named after the Greek god of wealth. It is a functional programming language based on Haskell, which provides enhanced security by making contracts easier to formally verify. Some key features of Plutus include:

– Validators – Functions that validate blockchain transactions via scripts.

– Datums – Inputs submitted to validators when transactions occur.  

– Redeemers – Claimable outputs locked to datums. 

– Functions – Contract logic that determines if/how redeemer claims datum.

Many projects are already leveraging Plutus to build decentralized apps and services on Cardano, such as decentralized exchanges, NFT marketplaces, identity solutions, traceability apps, and more. With robust research and academic rigor behind its design, Cardano aims to support global-scale applications.

For learning Plutus, the IOHK development team has released documentation on the language along with learning resources and workshops for developers. The Plutus Pioneer Program also helped onboard over 1,000 developers. As Cardano continues to mature, Plutus stands to become a major language for crafting secure and formally verified smart contracts.

Polkadot

Polkadot offers another much-anticipated blockchain project, founded by Ethereum co-founder Gavin Wood. It provides a sharded heterogenous multi-chain framework, where customized parachains (parallel chains) can connect to and leverage security from the primary Polkadot relay chain.

The Polkadot codebase is primarily comprised of Rust and Substrate – a blockchain development kit also created by Gavin Wood. Substrate provides modules for core components like consensus, accounts, tokens, governance, etc. which developers can configure and extend.

Smart contracts on Polkadot parachains are programmed in a language called Ink!, which is an eDSL (embedded domain-specific language) built in Rust. Ink! provides a Rust-like syntax for writing WebAssembly based contracts. Some key features include: 

– Storage items – Declare contract storage variables.

– Messages – Functions that can modify contract state. 

– Events – Emit events for other contracts to handle.

– Macros – Used to simplify repetitive logic.

– Functions – Internal logic that runs independently.

With this stack, developers can build custom blockchains that connect as parachains to relay chain security and interoperability. Existing examples include Acala (DeFi hub), Moonbeam (Ethereum-compatible smart contract platform), and more. Polkadot also supports bridges to external chains like Ethereum and Bitcoin.

For those interested in building on Polkadot, the Polkadot Builders Starter Guide provides useful tutorials and documentation on Substrate, Ink! and WebAssembly. As parachain deployment increases, Polkadot aims to serve as the backbone for an entire multi-chain ecosystem.

Cosmos

Cosmos offers another approach to blockchain interoperability, without relying on a central hub chain. Instead, it enables independent parallel blockchains to transact through Inter-Blockchain Communication (IBC) protocol. 

The Cosmos SDK is a generalized framework for building custom blockchains, each with their own validator sets and transaction logic. It offers modular capabilities like staking, governance, name registration, token management and more. Smart contracts and chain logic are written in Go, making the SDK accessible for mainstream developers.

Some key Cosmos SDK concepts include:

– Modules – Each manages specific domain logic like accounts, tokens, voting etc.

– Messages – Transactions that trigger state changes on blockchains.

– Handlers – Implement message processing logic via Go functions. 

– Queriers – Read-only handlers to query blockchain state.

– IBC – Handles communication between blockchains.

Numerous blockchains have already been built using the Cosmos SDK, including Terra, Crypto.com, Binance Chain and more. For those interested in learning, Cosmos SDK documentation offers excellent tutorials and concept explanations for getting started. There are also developer communities and events to help builders learn together.

Conclusion

This guide provides a comprehensive overview of today’s most prominent blockchain platforms and programming languages. While no single technology will definitively win out, understanding the differences in capabilities, architecture and use cases is important. Some key takeaways include:

– Ethereum leads for public smart contract development, especially in DeFi.

– Hyperledger Fabric excels for private consortium blockchains and enterprise apps. 

– Cardano offers research-driven design and focus on security and scalability.

– Polkadot facilitates cross-chain composability and parachain customization.

– Cosmos SDK enables building application-specific blockchains with IBC.

As blockchain adoption grows, we will continue to see new platforms, languages, tools and frameworks emerge. Factors like community support, documentation, and real-world usage will determine long-term success. For those exploring development today, this guide highlights plenty of options to get started building the next generation of blockchain innovations.