Half-Life: Hostile Takeover
Half-Life: Hostile Takeover was developed by 2015 but was never released or officially announced. In November 1999 GameSpot reported that 2015 was developing a new Half-Life expansion (Ajami, http://headline.gamespot.com/news/99_11/23_pc_halfadd/index.html). In March 2000 Adrenaline Vault reported that the game was titled Half-Life: Hostile Takeover and that it was to be released in August 2000 (Laprad, http://avault.com/news/displaynews.asp?story=3182000-91229). In August 2000 its cancellation was confirmed by publishers Sierra (Laprad, http://avault.com/news/displaynews.asp?story=872000-133010). The reasons for its cancellation are unknown but there is speculation that either Valve or Sierra did not want to flood the market with Half-Life expansion packs.
Although Half-Life: Hostile Takeover was never officially announced and no media was ever released, in spite of the short peiod between its announcement and reported release date, in the following years various details were gleaned from former 2015 developers: "was said to be 60% done and only 90 days away from going gold"; the player was to play a "Junior G-Man" type character; the game was initially set in the Black Mesa research facility but was changed to be set in Allied Processing (a support facility); new enemeies were to include a big houndeye and zombie monkey and new weapons were to include a vortigaunt gun and remote-controlled car-bomb (https://combineoverwiki.net/wiki/Half-Life:_Hostile_Takeover).