Also check out Simon Schneegan's spectacular work on FlyPie, OpenPie, Gnome-Pie, and his Coral Menus and Trace Menus:
https://schneegans.github.io/news/2020/08/13/flypie
http://schneegans.github.io/news/2020/10/10/flypie3
http://schneegans.github.io/news/2018/05/31/openpie
http://schneegans.github.io/gnome-pie
http://schneegans.github.io/news/2017/07/09/gnome-pie-071
https://schneegans.github.io/news/2012/10/10/bachelor-thesis