Half-Life is probably one of the modded games ever. The modding community is so active that several of the mods turned into retail games that are now considered classics.
Counter-Strike
Before Counter-Strike was one of the biggest esports ever it was first a mod of the original Half-Life game. The mod was first released on November 9, 2000, by a group of modders. The game received several updates and developed its own esports community. However, the game became so big that Valve bought the IP for the game. Counter-Strike received several sequels including the extremely popular Counter-Strike: Global Offensive.
USS Darkstar
USS Darkstar is a mod that is heavily inspired by the movie Alien and was built on the same engine as the original Half-Life. This game was a quick success and was showcased by Valve in 1999 as a part of a mod expo. Besides that, the game was also distributed by PC Gamer as a part of their magazine.
Day of Defeat
Day of Defeat started as a mod of Half-Life in 2000. The game went through several different iterations. However, the game became big enough that it was eventually bought by Valve. Besides that, the game had a remake called Day of Defeat source. The game is set in WWII and has no single-player elements.
Ricochet
Ricochet is a deathmatch game that has a similar vibe to Tron, and other futuristic games. The game was first released on November 1, 2000, and is a mod of the original half-life game. The game is very simple and has kind of been forgotten because of this. However, it can be a fun game to play, but don’t expect it to age wonderfully.
The Ship
The Ship started out as a Half-Life mod and was eventually turned into a full-on retail game two years later. The game is similar to the party game Werewolf or Mafia. This is a game that people may not have heard of, but it really is a good time to play!
Sven Co-op
Sven Co-op is a two-player mod of the original half-life which is still in development. However, it is well known for having one of the longest development histories of a mod. The game first started on January 19, 1999, and has been developed ever since.
Garry’s Mod
Garry’s Mod is one of the most popular games on the Steam store, and since the November 29, 2006 release of the game. The game is the origin of several staples such as Trouble in Terrorist Town and Prop Hunt. The game is the blueprint example of a game that spawns more game modes. However, it was released around the same time as other games of this archetype.
Dear Esther
Dear Esther was released in 2011, as a mod of Half-Life 2. However, the game was later released on the Steam storefront as a retail game. The game is the “walking simulator”, and created a lot of controversy around the genre when it was released.
The Stanley Parable
The Stanley Parable is another classic walking simulator game. However, this game is known for being one of the most experimental hit games of the 2010s. It is still beloved to this day. Despite this, most people don’t know that it was a Half-Life 2 mod.
They Hunger
They Hunger is a horror mod that was released in several parts in 1999. However, The game became very popular and is an example of early modding in the Half-Life community. Quake set the groundwork for a game with a great modding community. With the release of They Hunger the wheels started to move fast in the half-life community.