Unreleased Half-Life games

Half-Life is a series of first-person shooter games created and published by Valve. Since the release of the original Half-Life for Windows in 1998, several ports, expansion packs and sequels have been canceled, including projects developed by other studios.

In 1999, Valve canceled a Half-Life port for Mac developed by Logicware. Half-Life: Hostile Takeover, an expansion pack for Half-Life developed by 2015, Inc, was cancelled in 2000. In 2001, Sierra, the publisher of the original Half-Life, canceled a port for Dreamcast after Sega announced its discontinuation.

After releasing Half-Life 2: Episode Two in 2007, Valve struggled to settle on a direction for a new Half-Life game. Episode Three was canceled after Valve abandoned episodic development and began developing a new game engine, Source 2. Another Half-Life 2 episode, by Junction Point Studios, was canceled after Junction Point was acquired by Disney Interactive Studios. Valve moved the project to Arkane Studios, who developed it as Ravenholm, set in a town infested with zombies. Valve canceled it as they felt it was creatively restrained.

Valve developed Half-Life 3 between 2013 and 2014, experimenting with procedurally generated levels, but canceled it as the Source 2 engine was still unfinished. A virtual reality (VR) game set on a time-travelling ship, Borealis, was canceled as the VR technology and tools were not complete.

Half-Life: Hostile Takeover
On November 23, 1999, GameSpot reported that 2015, Inc. was developing a Half-Life expansion pack to follow Half-Life: Opposing Force. 2015, Inc declined to comment. On March 18, 2000, the Adrenaline Vault reported that the new expansion was named Half-Life: Hostile Takeover, and that it had appeared on retail product lists with a release date of late August. On August 7, the Adrenaline Vault reported that Sierra, the publisher of Half-Life, had informed them that Hostile Takeover had been canceled. The stock keeping unit for Hostile Takeover was repurposed by online retailers for Half-Life: Counter-Strike. On June 21, 2001, Valve filed a video game trademark for "Hostile Takeover". After several extensions, the trademark expired on October 3, 2004.

Dreamcast port
On February 14, 2000, Sierra announced that a port of Half-Life for the Dreamcast console was in development by Captivation Digital Laboratories with Valve and Gearbox Software. The Dreamcast port would feature improvements including higher-polygon characters and new lighting effects. Gearbox, who had developed Opposing Force, created a new single-player campaign for the Dreamcast port, Half-Life: Blue Shift, focusing on the security guard Barney.

The port was delayed to September 2000, then November, when game publications began to receive early copies for review. Reception was mixed, with criticism for the inconsistent frame rate, long loading times and lack of online play. Sierra planned to release a version with online multiplayer using SegaNet. The Gearbox CEO, Randy Pitchford, said he suggested including additional multiplayer modes and mods from the Windows version, including Team Fortress Classic and the multiplayer modes from Opposing Force. Sierra delayed the port again to ensure that it met the "high expectations of consumers", and said they hoped to finish development that year.

On March 29, 2001, Sierra announced that Blue Shift would be released for Windows along with the new models developed for the Dreamcast version, as part of the Half-Life High Definition Pack. On June 16, 2001, four days after the release of Blue Shift, Sierra announced that it had canceled the Dreamcast port, citing "changing market conditions". It was weeks away from its release date and virtually complete. In 2013, a late version of the Dreamcast port leaked online, featuring complete versions of Half-Life and Blue Shift.

Mac port
A version of Half-Life for Mac OS was announced by Logicware on April 23, 1999. However, Valve canceled it a few months later in October 1999. The Valve CEO, Gabe Newell, said the port was substandard, citing a separate multiplayer network, no automatic update utility and the inability to include Valve's multiplayer mod Team Fortress Classic. He said he did not want to make Mac players "second-class customers" and preferred to write off the investment rather than "take money from Mac customers and short-change them". Rebecca Heineman, the co-founder of Logicware, denied this, saying that Valve cancelled the port as Apple had angered them by misrepresenting sales projections. She said the port was complete and three weeks from release. In 2013, Valve released a port for OS X.

Half-Life 2: Episode Three
In May 2006, Valve announced a trilogy of episodic games that would continue the story of Half-Life 2 (2004). Episode One was released in 2006, followed by Episode Two in 2007. Episode Three was initially announced for Christmas 2007 and was highly anticipated. Valve released little information in the following years, and in 2011 Wired described it as vaporware.

Valve eventually abandoned episodic development, as they wanted to create more ambitious games. The designer Robin Walker said Valve failed to find a unifying idea for Episode Three that provided a sense of "wonderment, or opening, or expansion". Additionally, they had started developing a new game engine, Source 2. As developing Half-Life 2 and the original Source engine simultaneously had created problems, Valve delayed development of a new Half-Life until Source 2 was complete.

Junction Point Studios episode
Another Half-Life 2 episode was developed by Junction Point Studios, led by Warren Spector. The episode showed how Ravenholm became the town seen in Half-Life 2, infested with headcrabs and zombies, and saw the return of the character of Father Grigori. It included a "magnet gun", which fired projectiles that magnetized metal surfaces and attracted objects and enemies, and would have been used for combat and puzzles.

Junction Point worked on the game for a year, producing enough content to demonstrate one section, and a vertical slice that demonstrated the magnet gun. Valve lost interest in the project and Junction Point, who had been acquired by Disney Interactive Studios partway through, canceled it to instead develop Epic Mickey. Images of the game appeared in early 2017.

Ravenholm
In 2007 or 2008, Valve gave the Junction Point project to Arkane Studios in Lyon, France. They developed it into a standalone game with the working title ''Ravenholm.  It was also referred by some sources to as Episode Four.''

Players controlled Adrian Shephard from Opposing Force, working alongside Father Grigori, who had taken refuge in an abandoned psychiatric hospital. Grigori was experimenting with the effects of headcrab venom on himself, and would mutate through the story. The player would use the magnet gun and traps created by Grigori against enemies. Arkane also implemented a nail gun that could create paths to conduct electricity and set traps.

Valve gave Arkane freedom to develop Ravenholm, as they had with Gearbox and Opposing Force, providing feedback and technical support. With approximately one year left of development, Valve canceled the project. The Arkane founder, Raphaël Colantonio, believed that Valve decided it would be too expensive, and Laidlaw said that Valve felt the premise was creatively constrained. Ravenholm was first shown publicly in a 2020 Noclip documentary. Noclip released an hour of gameplay footage in 2022.

Half-Life 3
Half-Life 3 was in development between 2013 and 2014. Valve planned to use procedurally generated levels alongside a "crafted experience", similar to the Left 4 Dead series; for example, the game would generate different routes through environments each time it was played. The team took new scans of the face of Frank Sheldon, whose likeness was used for the G-Man character in Half-Life 2. The Source 2 engine was still unfinished and the project was canceled early in development.

Borealis
Before his departure from Valve in 2016, Laidlaw led a virtual reality project on the Source 2 engine, Borealis, set on the time-travelling ship mentioned in Episode Two and Portal 2. The game would skip between the Combine's conquering of Earth before Half-Life 2 and a time set shortly after Episode Two. A minigame in which players would fish off the bow of the ship was also proposed. Laidlaw said the project ended because it was too early to be working in VR: "When people are struggling with the basic tools they need to rough out a concept, it's hard to convey any sort of vision, and it all evaporated pretty quickly."