Ubuntu 12.10 comes with a new Unity webapps features that allows you to integrate your favorite websites with Ubuntu desktop.
These webapps are installed on your desktop like native apps, they can be pinned to launcher and can be used with messaging menu, sound menu, HUD etc. When you visit a website that have Unity webapps support, you will get a prompt like this:
After installing a webapp, if you want to remove it for some reason, you can follow the steps below.
First, launch Ubuntu Software Center and check that a package for specific webapp is installed or not. Just remove the concerned package.
Next launch dconf editor from dash and go to com > canonical > unity > webapps. In allowed-domains, remove the entry which you don't want.
Lastly, go to ~/.local/share/applications and remove the .desktop file for the webapp you would like to uninstall.