Linux Ubuntu Emacs with https://tuhdo.github.io/c-ide.html

Ros (Robotics stack)

OpenCV (from source)

Caffe

PointCloud

Google benchmark and Google test

Linux perf tools (I am one crazy measuring geek)

GCC (latest version from source)

LLVM (Same ^^^)

and one that I don't use that much is radare2 since I am reverse engineering hobbyist.