From Gentoo Wiki
Piper is a GTK+ application to configure gaming mice. Piper is merely a graphical frontend to the ratbagd DBus daemon.
USE flags for app-misc/piper GTK application to configure gaming devices
|Enable dependencies and/or preparations necessary to run tests (usually controlled by FEATURES=test but can be toggled independently)
emerge --ask app-misc/piper
For non root access to ratbagd user should be in group
usermod -aG plugdev larry