The "Who's That" service is a database of all names users had since the beginning of the project. It tracks renamings and shows when a particular user was active and under which name. On the front page it displays users who last renamed themselves.
|License:||WTFPL (free of charge)|
|Programming languages:||Perl and PHP|
The service relies on the fact that the sixth version of the API publishes the user's display name as well as its stable user ID in each changeset a user uploaded. This is also the suggested mechanism to reliably identify users in the API documentation. However, users who renamed their accounts and never uploaded changesets afterwards will not have their user names published in this service. Knowing the user's ID, one can query the current display name. Who's That does not seem to use this API query.