Looking for logging into the Developer Force site and are not getting the correct working link for it? In such a case, you can use the links given here by searching your desired login page in the search box. If the page is present on our website then you will get all the links related to the Developer Force site. After that you can login as usual with your login credentials.
https://login.salesforce.com/?locale=de
https://developer.salesforce.com/
http://developer.force.com/chatterdevchallenge/challengeLogin
https://workbench.developerforce.com/
https://developers.facebook.com/docs/reference/javascript/FB.getLoginStatus/
https://github.com/forceworkbench/forceworkbench/wiki
https://developers.gigya.com/display/GD/Social+Login
https://developers.google.com/+/web/signin/
https://salesforce.stackexchange.com/questions/60370/login-to-workbench-returns-an-error-oauth-app-access-denied-user-is-not-admin
https://auth0.com/docs/connections/social/facebook
https://www.nvidia.com/en-us/account/redeem/
https://developer.jboss.org/thread/149588
https://www.mockplus.com/blog/post/sign-up-login-design-practices