cboy is a Game Boy emulator written in C for GNU/Linux.
cboy bootrom.bin game.gb
You'll need a compiler and SDL2. On Debian, you can install all dependencies with
sudo apt-get install build-essential libsdl2-dev
Then, to build cboy:
cd src
make
Most of cboy is GPLv3, however the gb_apu library from Shay Green is LGPL.