It’s a pretty old Source Engine game. Can run on a potato PC.

From Steam:

OS: Windows® 7 32/64-bit / Vista 32/64 / XP

Processor: Intel core 2 duo 2.4GHz or AMD Athlon 64 X2 4600+

Memory: 1 GB for XP / 2GB for Vista

Hard Disk Space: At least 6 GB of free space

Video Card: : DirectX 9 compatible video card with Shader model 3.0. NVidia 7600, ATI X1600 or better

DirectX®: 9.0c

Sound: DirectX 9.0c compatible sound card

Additional: Internet Connection required for multiplayer