KeePassXC seems to have been forked from KeePassX because of the slow development of KeePassX (it's last update was v2.0.2 on ) while KeePassXC started with v2.1.0 on. After KeePass/L became a cross platform application the name was not appropriate anymore and therefore, on 22 March 2006 it has been changed.

Originally KeePassX was called KeePass/L for Linux since it was a port of Windows password manager Keepass Password Safe. It is now available as a native program for Linux, Windows, OS X, and others. KeePassX is an 'Contributed/Unofficial KeePass Port' of KeePass that was started in 2005 (if the copyright notice on the bottom of their webpages is accurate) to run KeePass on Linux.

KeePass was started about 2003, originally for Windows only, but now uses Mono to run on anything that Mono supports, like Mac OS X, Linux, FreeBSD. user names, passwords, urls, attachments and comments. You probably already know, but both KeePass and KeePassX (& now KeePassXC, a fork of KeePassX) are open source (published under the GNU General Purpose Licence 2) secure (using AES or Twofish) data storage programs, using a single database file to store (mainly) passwords, or pretty much any data you'd like e.g.

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