Plan of Attack

Single-player mods

Aperture Tag - A modification based on Portal 2 that recreates the essence of the game Tag: The Power of Paint, the inspiration for the various gels used in Portal 2. Instead of a portal gun, the player solves puzzles using a mix of these gels that they can spray onto surfaces with a tool they carry.

Black Mesa - A third-party recreation of Half-Life (1998) that was made in response to the release of Half-Life: Source (2004), a port of the original game to the Source engine. Black Mesa originally released as a free mod in September 2012, and later had a full commercial release on Steam in March 2020.

Coastline to Atmosphere - A mod set in the Half-Life 2 universe, following Gordon Freeman after the events of Half-Life 2.

Dear Esther - An experimental "ghost story" created as a research project at the University of Portsmouth; initially released as a free modification in 2008, a longer commercial version was developed and released in 2012.

Entropy: Zero - A Half-Life 2 modification developed by Breadman set before the base game's story in which a Combine Civil Protection officer, named "Bad Cop", becomes stranded in City 10.

Entropy: Zero - Uprising - A mod of Entropy: Zero developed by Employee8 and Filipad that takes place during the uprising in Half-Life 2.

Entropy: Zero 2 - A sequel to Entropy: Zero. Set post-Half-Life 2, its story follows Bad Cop, who has been promoted to "Elite" status, as he works to capture Dr. Judith Mossman, the former assistant of Earth's Administrator. Developed over the course of five years, Entropy: Zero 2 was released in August 2022 to positive reviews on Steam, and went on to win Mod DB's 2022 "Mod of the Year" award in the "Players Choice" category.

Flipside - A side-scrolling platform game that allows the player to "flip" the game world around to its backside, altering the means a player can traverse a level.

Half-Life 2: Overcharged - A single-player mod for Half-Life 2 that adds new enemies and locations as well as cut content, extending the base game. Originally released in 2022, the mod gained notoriety in 2024 due to the mod developers blacklisting content creators that criticized the mod by targeting their Steam IDs and crashing their game. This led to the mod being review bombed on Mod DB.

Jurassic Life - A modification based on the first Jurassic Park film. The game acts as a side story to the movie where the player takes the role of the park's game warden, Robert Muldoon.

Korsakovia - A single-player mod for Half-Life 2. It was developed by The Chinese Room and released September 19, 2009. In Korsakovia, the player travels through the delusions of Christopher, a man suffering from Korsakoff's Syndrome. The player hears the voices of Christopher and a doctor as they try to work out what is wrong with Christopher.

Minerva - An episodic single-player mod based in the Half-Life 2 universe, using storytelling inspired by classic games such as Marathon and System Shock.

Operation Black Mesa - An upcoming remake of the Half-Life expansion Opposing Force developed by Tripmine Studio.

Portal: Prelude - An unofficial prequel to Portal, set before the activation of GLaDOS when scientists used to watch over the test chambers and instruct the test subjects.

Portal Reloaded - A mod atop Portal 2 that introduces the ability to place a third portal that sends the player-characters or objects through between the present and a future state of the same test chamber. Actions in the present state will alter the future, though manipulation of the future situation will not impact the present, allowing, for example, for one to bring a weighted cube set in the present from its position in the future, back through the time portal, and use that version of the cube in the present.

Portal: Revolution - A mod build on Portal 2 by Second Face Software, in which the player controls an anonymous test subject in the destroyed Aperture Science laboratories. The player is tasked to repair a teleportation device. The mod is set in between the events of Portal and Portal 2.

Portal Stories: Mel - A mod build on Portal 2, in which the player controls Mel, a female test subject who is named after a character that Valve had originally designed for Portal 2's cooperative mode. It is a fan-made mod that takes place after the events of Portal and before the events of Portal 2.

Prospekt - A fan-made sequel to Half-Life: Opposing Force that follows its protagonist, U.S. Marine Adrian Shepherd, as he is sent to help Gordon Freeman during the "Nova Prospekt" segment of Half-Life 2.

Research and Development, a "non-combative" modification that has been likened to Portal, in which the player uses the gravity gun and other aspects of the Source engine physics to solve puzzles and progress forward.

Rexaura, a Portal modification developed by Ben "Mevious" Bryant featuring 20 (from 00 to 19) puzzles designed around manipulating and ricocheting energy pellets.

Riot Act - A mod set in the Half-Life 2 universe, following a member of the civilian resistance on their escape from the Combine prison at Nova Prospekt.

The Stanley Parable - An interactive fiction modification, with multiple endings depending on decisions made by the player. Similar to Dear Esther, the mod was developed into a full commercial release in 2013.

Thinking with Time Machine - A mod built atop Portal 2, which adds in the ability for the player to create a brief recording of their actions and then interact with that recording on its playback, including the use of portals.

Multiplayer mods

Age of Chivalry - A multiplayer modification. Players fight for either the Mason Order or Agathian Knights in a fictional medieval environment using swords, spears and many other medieval weapons. The mod was released on September 10, 2007. Age of Chivalry received Mod DB Editor's Choice for 2007.

Counter-Strike: Malvinas - A multiplayer first-person shooter modification of Counter-Strike: Source, developed and distributed by Argentine web hosting company Dattatec. The game is set in Stanley, the capital of the Falkland Islands. The objective of the game is same to that of the Counter-Strike series; each round is won by either detonating a bomb or by eliminating all members of the enemy team. The mod prompted strong controversy in the United Kingdom; Dattatec's website was targeted by British hackers on March 27, 2013.

Dino D-Day - The game is set in 1942 during World War II. The premise of the game is that Adolf Hitler has resurrected dinosaurs, and players can battle online choosing to serve either the Allied nations or the Nazis.

Dystopia - A cyberpunk-themed total conversion, somewhat based on popular role-playing game Shadowrun, that pits Punk mercenaries against corporate security forces in both the physical world and cyberspace. Last release August 23, 2014. Dystopia received the Player's Choice Honorable Mention from Mod DB in 2006, Best Mod for Half-Life 2 during the Independent Games Festival in 2006, and received the "Mod Of The Year - 3rd place" and "Genre Award - Action" for mods of 2005 by Mod DB.

Empires - A first-person shooter/real-time strategy hybrid where each team led by a commander, viewing the world in the top-down perspective leading troops in the first-person perspective. It features a variety of player classes and vehicles. Empires has received media coverage from IGF, PC Games magazine, PC Action magazine, SteamFriends, and Planet Half-Life. It was also awarded the "Genre Award: Multi-Genre" from Mod DB in 2006, won 3rd place Player's Choice at Mod DB's MOTY awards 2007, and received a Silver award from SteamFriends as 2nd best Source mod of 2007.

Eternal Silence - A hard science fiction, class-based first-person shooter featuring infantry and space combat scenarios. Eternal Silence pits two capital ships of rival factions against one another for domination of human-occupied space. It won "Best Mod - Multiplayer FPS" during the Independent Games Festival in 2006, "Best Multiplayer Mod of the Year - Honorable Mention" from Mod DB in 2006, and "Mod DB Editors' Choice Award" in 2007.