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.