The Xposed Framework lets you modify your phone's software like nothing else. But because of how powerful this tool can be, it seems like things are always in development. This is certainly the case with many Xposed modules, to the point where some have several alpha and beta releases before they go mainstream.
The Xposed Framework is still alive and kicking despite the fact that development has slowed down a bit lately. Rovo89 is the only true developer behind Xposed, so it's really a one-man show. This means the popular root mod doesn't typically support the latest Android version, but it's usually only one version number behind.
The Xposed Framework is a very powerful platform on top of which smaller modules can run to make changes to the Android system and various other apps. Installing modules is just as easy as sideloading any Android app, but afterwards, you'll need to activate the module and reboot your device.