Black Mesa Sideline is a small Half-Life singleplayer mission. It contains 2 maps and is fully compatible with HL-Steam and HL-Won.

poshgaloo says

9/10 - Agree (1) Disagree

Pros:
GREAT MAPPING!!!
Fun gameplay!!!
Classic location!
Cons:
WAY TOO SHORT!!! It's only 2 maps. :(