WordPress.org is a blogging platform that is owned and hosted online by Automattic. It is run on a modified version of WordPress, an open source piece of software used by bloggers. This website provides free blog hosting for registered users and is financially supported via paid upgrades, “VIP” services and advertising.
The site opened to beta testers on August 8, 2005, and opened to the public on November 21, 2005. It was initially launched as an invitation-only service, although at one stage, accounts were also available to users of the Flock web browser. As of February 2017, over 77 million new posts and 42.7 million new comments are published monthly on the service.
This maintenance release fixes 33 bugs, including improvements to the block editor, accessibility, internationalization, and the Site Health feature introduced in 5.2.
You can browse the full list of changes on Trac.