
Cry of Fear does not require Half-Life to be installed. It’s completely stand alone as a full game, and it’s completely free!
Cry of Fear is a psychological single-player and co-op horror game set in a deserted town filled with horrific creatures and nightmarish delusions. You play as a young man desperately searching for answers in the cold Scandinavian night, finding his way through the city as he slowly descends into madness.

This game is StandAlone (doesn’t require HL2) BUT requires Steam and Source SDKbase 2007 installed (both FREE)
GoldenEye: Source is a total conversion modification of Half-Life 2. It is a fan made recreation, released for free, with only one goal in mind; to bring the memories and experiences from the original GoldenEye64 back to life using Source Technology.

Pirates, Vikings and Knights II is a first-person melee combat game built on Valve’s Source engine. PVKII is free to download and play.

Ur-Quan Masters v0.7.0 is a port of The Ur-Quan Masters, using SDL, targetted for Linux, all BSD, Windows, MacOS X, and other SDL-supported platforms.
Ur-Quan Masters HD Mod is an HD remake of Star Control 2. It’s the full Ur-Quan Masters game but also featuring a high resolution mode, new features, and new artwork.
The UQM-Mods project is a collection of 3 mods that allow players to “enhance” gameplay or to add features that were otherwise unavailable. For Ur-Quan Masters v0.7.0

SweetFX is a program that helps refining how your game looks, you can control effects like blur, AA, SMAA, FXAASMAA (anti aliasing), sharpening, vibrance, tonemap, curves, HDR, bloom – and more!
It seems that the frames per second drops is minimal.