web3 is a library to communicate with Ethereum nodes, and there are web3.py and web3.j projects centered on web3.js. It is a project underway by the Ethereum Foundation, and all are open source, so anyone can contribute.
Remix: IDE for writing Solidity Smart Contracts
Etherscan: Blockchain Explorer
Metamask: Ethereum wallet for chrome extension
EtherID : Ethereum ID Registar
Etherflip : Ether gambling Dapp game / eth casino
Etherapis : Micropayment platform for generic API calls
Ethereum-grove : Fast, efficient, queryable storage for ethereum contracts.