The official Steam or GOG version (it runs on almost anything).
Be cautious of sites offering a "Broforce Portable" .exe file for free. Aside from the official or the Free Lives alpha , these are often pirated versions of the full game and may contain malware. Supporting the developers by purchasing the full game on Steam gives you access to the Broforce Forever update, which includes dozens of extra characters and a full campaign. broforce free play portable