is an extension that allows a user with permission to check which IPs are used by a given username and which usernames are used by a given IP, without having to run queries directly against the database by hand.
Status: stable
Developer: Tim Starling, Aaron Schulz
Extension type: MediaWiki
Edition: BlueSpice free
License: -"-" is not in the list (ISC, MIT, WTFPL, GPL v2+, GPL v2+ and MIT, GPL v3+, GPL v3, GPL v3 only, GPL v2+ and BSD 3 Clause) of allowed values for the "BSExtensionInfoLicense" property.
Activated: -"-" is not recognized as a Boolean (true/false) value.
Category: -

CheckUser enables you to check the IP address and other information of users. Users who are part of the "Checkuser" group can check the allocation of IP addresses and user names (and vice versa) without having to access the database. By the way: this is a feature also used by Wikipedia.

For more information please visit MediaWiki.