ABI Ninja lets you interact with any contract on Ethereum:

• Verified contracts (pulls the code from the Etherscan API)
• Unverified contracts (providing the ABI)

It includes nice features like: (mainnet!) ENS resolution on address inputs, shareable URLS, navigation, show tx results, etc.

Still a WIP. Current state: https://abi.ninja (GH: https://github.com/carletex/abi.ninja)