Hi Mahias,
To remove aiStarter on Mac OS X, you can do the following:
1. Open Finder and browse to Applications. There will be a folder called AppInventor.
2. Move the AppInventor folder to the Trash. You may need to provide your password to authorize this.
3. Press Cmd+Shift+G to open the "Go to the folder" dialog. Enter /Library/LaunchAgents/
4. If there is a file called edu.mit.appinventor.aiStarter.plist, move it to the Trash as well.
After deleting the files above, you should restart your computer.
Evan