You might not even remember this one. Standalone Half-Life 2 mod NeoTokyo was first released way back in 2008, but now the tactical cyberpunk shooter is available .
As it's a standalone mod you can download it for free, and you won't need to own any other Source Engine-powered games for it to work.
NeoTokyo is set (as you might have guessed) in a near-future version of Japan, currently embroiled in a violent military coup. You play as either the loyalist NSF or rebellious JINRAI, doing battle with high-tech weapons and gadgets across various futuristic urban levels.
It's a tense, slow-paced affair in which you need to be constantly aware of your surroundings. Well worth a look if you're in the mood for a tough, uncompromising multiplayer experience with an impressively realised setting.