Which software can I use to setup an e-wallet site? I am relatively new to Bitcoin and I have a very simple question: what wallet software is behind "online wallet sites" like http://www.blockchain.info? I would like to set up a mini-site to store my/friends online wallets and I guess I would need a daemon-shell-based Bitcoin wallet software.

Where should I start to do so?
Most eWallet services would probably be using the standard Bitcoin client running in the server mode. You would then control it through the use of the JSON RPC commands.

But for personal use, you probably want to just use existing eWallet solutions, or commission someone to help you set your wallet up taking into account such concerns as data security, proper wallet backup and so forth (shameless autopromotion - you can contact me;) ).