A curated list of bitcoin services and tools for software developers:

 

Utilities

• Pycoin Python-based Bitcoin and alt-coin utility library.
• sx sx - command line Bitcoin to empower the sysadmin
• bx Bitcoin Command Line Tool
• txwatcherA little Python utility that lets you monitor Bitcoin addresses through Blockchain Websocket API and perform custom callbacks.
• hellobitcoin  A collection of simple programs which can generate bitcoin wallets,  create and sign transactions, and send transactions over the bitcoin  network.
• Mining visualization

Blockchain API and Web services

• block.io
• BlockCypher
• Gem.co
• Insight
• Chain.com
• Toshi by Coinbase
• Smartbit

Wallets API

• BitGo
• Coinbase
• Blockchain.info
• BIP32

Open Source Wallets

• CoPay by BitPay
• CoinPunk
• Coinb.in
• Electrum

Blockchain Explorers

• Chain.so
• Blockchain.info
• BlockTrail 
• Blockr
• Bitcoin Transaction Explorer
• Blockexplorer.com
• Smartbit

JavaScript Libraries

• Awesome CryptoCoinJS
• Bitcore Library
• Bitcoinjs-lib
• Cryptocoin
• BlockTrail SDK NodeJS

PHP Libraries

• PHP-OP_RETURN
• BlockTrail PHP SDK

Ruby Libraries

• Bitcoin-ruby

Python Libraries

• BlockTrail SDK Python
• btctxstore simple library to store/retrieve information in bitcoin transactions using OP_RETURN

Java Libraries

• BitcoinJ

.Net Libraries

• NBitcoinComprehensive Bitcoin library for the .NET framework.
• BitcoinLib The most complete, up-to-date, battle-tested .net Library and RPC Wrapper for Bitcoin and Altcoins in C#.
• QBitNinja An Open Source and powerful blockchain API

Playgrounds

• Script Playground
• Bitcoin IDE Bitcoin Script for dummies
• Debug Script Execution
• Bitcore Playground
• Mnemonic Code generator

Blockchain dump

• WebBTC These are postgres database dumps of the bitcoin-ruby-blockchain database generated by webbtc.com.
• BitcoinDatabaseGenerator A high performance data transfer tool that can be used to copy data from Bitcoin Core blockchain files to a SQL Server database
• Blockparser+SQL Fast, quick and dirty bitcoin blockchain parser
• BitcoinABE Abe: block browser for Bitcoin and similar currencies
• NBitcoin.Indexer Scalable and fault-tolerant block chain indexer for Azure cloud platform.

Full nodes

• Bitcoinjs-server Bitcoin network node in JavaScript using Node.js / LevelDB
• Bitcoin-ruby-node bitcoin node based on bitcoin-ruby-blockchain
• Toshi by Coinbase An open source Bitcoin node built to power large scale web applications
• Fullnode Javascript implementation of bitcoin
• Insight API A bitcoin blockchain API for web wallets
• Bitcoind.JS bitcoind linked to node.js by BitPay
• Bitcore Formerly just a Nodejs library, now a full node

Read

• Mastering Bitcoin
• Bitcoin Stackexchange
• Elliptic Curve Cryptography A Gentle Introduction