Black Mesa: Sideline is a small Half-Life singleplayer mission. It contains 2 maps and is fully compatible with HL-Steam and HL-Won.
Extract the zipped package to your Half-Life folder in Steam or i.e. “..SierraHalf-Life..” in case you are using the won-version of HL. That’s it, have fun.
I created Black Mesa: Sideline to participate in a little Half-Life mappack project that was arranged by the german Half-life mapping community Thewall.de
in June 2007. In the end I wasn't able to finish my part of the project so I threw together what I had and released it without any story elements.
It turned out to be moderately successful and I am still very satisfied with the quality I accomplished back then.