Research and Development is a puzzle-centric mod for Half-Life 2: Episode Two featuring an unarmed player but plenty of violent mayhem.
Very, very fun mod. The puzzles are excellent and very creative. The puzzles are of equivalent quality to those in hl2, and occasionally much better. Although the description says the mod is puzzle based there are sections of combat that are as pulse-pounding as any in hl2. Hurl mines at enemies with the iconic gravity gun, careen through hazards in a runaway train car, and shred through enemies with an original vehicle unique to this mod.
My only complaint is that the health gauge on the HUD is gone, making it hard to keep track of your nonregenerating health (though because of the way the mod is designed it very rarely mattered). Also, the vehicle is occasionally hard to steer.