Mineshafter

Follow these steps to get up and running with Mineshafter:

1. Make sure that you have a Minecraft.net account (paid or not, doesn't matter).
2. Login. Done
3. Link your Minecraft.net account. Done
4. Upload a custom skin if you want one.
5. Upload a custom cloak if you want one.
6. Download the client proxy.
7. Start the proxy program, it will use the Minecraft launcher in the current directory or use the latest one from Minecraft.net if you don't have one.
8. Login with your Minecraft.net credentials.
9. You're client will update if not already at the latest version.
10. When done playing, close Minecraft.
11. Steps 4 and 5 are not required.

source :http://mineshafter.appspot.com/instructions