What: Classic FPS Sale
If you're planning on staying in during this ferociously hot weekend (and why wouldn't you, solar radiation is dangerous), GOG are running a FPS-themed promotion featuring some proper classics. Highlights include Duke Nukem 3D's Atomic Edition for £1.90, cel-shaded comic XIII for £1.90 and the deliciously sadistic Blood games.
It might also be a good time to pick up Unreal Tournament's GOTY Edition. For my money, that game still stands amongst the best multiplayer experiences ever crafted and still holds up brilliantly. M-m-m-m-m-monster kill!