The web is full of great free services. To save you having to create a new
username and password every time you sign up, many of them allow you to
optionally sign in with your existing account. But over time, you tend to
forget just how many of these services you have tried. In the case of Google,
check this out how to review and deny access to any of those with a single
click.
http://www.techsupportalert.com/content/do-you-know-how-many-apps-have-access-your-google-account.htm
