"Half-Life: Hostile Takeover is a cancelled Half-life game that only very little is known about. It was under development at 2015 inc. and was to feature the Team Fortress characters as the players sidekicks, let's have a look!

Furhter reading:

http://forums.steampowered.com/forums/showthread.php?t=920482
http://web.archive.org/web/20000301003051/http://headline.gamespot.com/news/99_11/23_pc_halfadd/index.html
http://web.archive.org/web/20000607145116/http://avault.com/news/displaynews.asp?story=3182000-91229
http://www.valvetime.net/threads/the-lost-half-life-expansion-pack.254612/
http://web.archive.org/web/20010521163812/http://avault.com/news/displaynews.asp?story=872000-133010"