Note that this GitHub repository is a bit unusual in that it does not contain any source code. It's purpose is solely for issue tracking. The idea is to have the complete list of all known bugs, issues, and possible improvements out in public, accessible to anybody.
Under Issues, you can find a list of all known issues and planned features.
Under Milestones, you can find a list of feature themes (topics, epics), together with milestones for the next upcoming releases.
Check the releases page for past and current releases.