This organization is the home of various Application Lifecycle Management (ALM) tools, mostly around Release Flow conventions.
The Keep-a-Changelog Action repo contains a GitHub Action to drive versioning from a changelog. It's not related to Release Flow, but it's kinda handy for some scenarios.
The releaseflow.org website describes a slightly different form of release flow, which is (as the site admits) just a 'trendy name for the Release Branching strategy'. This is unfortunate, as the form of Release Flow described on the Microsoft blog, and implemented here, is different in one crucial way: in true Release Flow, hotfixes to a release are first performed on the trunk branch then cherry-picked onto the release branch (with few exceptions). In the release branching strategy, they suggest to fix the release branch and then cherry-pick onto the trunk.