The game and its engine are 100% open source.
Connect two or more controllers for local multiplayer.
W,A,S,D - Movement
Q, E - Switch weapons
Click to Shoot
Space - Shield (for multiplayer)
Left Thumb Stick / Up, Down, Left, Right - Movement
Right Thumb Stick - Aim
RB, LB - Switch weapons
RT - Shoot
LT - Shield (for multiplayer)