The list is divided into two categories: clientside and serverside mods. These terms do not necessarily indicate whether each mod can be run on multiplayer servers. Clientside mods add content to the game, such as a new storyline, models or sounds. In contrast, serverside mods add functionality.
Afraid of Monsters – The original Afraid of Monsters was developed by the then-14-years-old-boy ruMpel, one of the leaders and founder of Team Psykskallar. A single-player horror mod. The protagonist is David Leatherhoff, a drug addict who must face his darkest fears; in a nightmare, the player must decide whether it is a drug hallucination or real. Unlike the Director's Cut version, it has only 1 ending.
Afraid of Monsters: Director's Cut – The improved version of Afraid of Monsters, developed by Team Psykskallar. The improved version features new enemies, models, animations and various improvements. It has four different endings.
Cry of Fear – The spiritual successor of Afraid of Monsters, it puts the player in the shoes of Simon, a paraplegic who writes a book for therapy, and in the process faces the inner demons that plague his thoughts. It features a co-op mode. Though initially a mod, it was later released as a free standalone game in 2013 via Steam.
They Hunger – This is a single-player horror-based mod. It was released by Neil Manke's Black Widow Games in three episodes, the first in 1999, the second in 2000, and the final installment in 2001. All three were at one point bundled with PC Gamer magazine.
USS Darkstar – This mod follows a scientist on a deep-space scientific mission aboard an interstellar spacecraft. When an experiment goes awry, the player has to defend himself against aliens. This mod was featured by the PC Gamer magazine on its demo CD in 2001.
Wanted! – A Wild West-style mod which follows a town Sheriff and his hunt for a bandit. Enemies include rattlesnakes, Native Americans and other outlaws. It contains original voice acting and era-specific weapons, and was created by Maverick Developments and released as a free mod. For some time it was bundled with the retail version of Counter-Strike, along with another mod by Maverick Developments, Absolute Redemption which was a chapter set between Half-Life and Half-Life 2.
Action Half-Life – A team-based multiplayer mod developed as part of the popular series of "Action" based mods, designed to emulate the feel of an action movie. Members of the development team had previously worked with developers of Counter-Strike on the mod Action Quake 2.
Counter-Strike – A team-based, hugely successful, tactical first-person shooter game involving rounds of combat between two teams, counter-terrorists and terrorists. It was originally a mod and later a commercially released game.
Team Fortress Classic – Originally a mod ported from QuakeWorld that introduced a class-system style of play that allowed for many diverse playing styles. With the introduction of Steam it became a standalone game and as of October 10, 2007 it has a commercially released sequel Team Fortress 2.
Global Warfare – A team play class based mod set in the Middle East with frantic gameplay and new features (e.g. troop transports taking players into battle).
Natural Selection – A mod in which two teams (humans and aliens) fight against each other. Its utilizes a mixture of first-person shooter and real-time strategy gameplay. It gained a standalone successor, Natural Selection 2.
Sven Co-op – A co-op mod in which players fight against computer-controlled enemies. Apart from user contributed missions it is also possible to play co-operatively through the original Half-Life game.
Master-Sword – A Roleplaying Game originally released in 1998, it has since gone through several revivals. Master-Sword has often been one of the most popular mods on ModDB and it is one of the few mods to still survive. 
The Half-Life serverside engine could originally only support one mod at a time, because it used to load a DLL which contained the standard engine as well as the mod.
Metamod is a serverside mod that fixed this, allowing multiple mods to be run at once. Many such mods run under Metamod, referred to as Metamod plugins.
The AMX Mod was a plugin running under Metamod that allowed scripts to be written for the servers. It got its name from the filename extension of compiled Pawn files, which stands for Abstract Machine eXecutive. In 2007 the AMX Mod project was merged into the related AMX Mod X, which had more features.
But in 2010, AMX Mod was brought back to life by a few people of fans. Then, in 2013 May 01, the new AMX Mod Team officially re-opened the old site with a design remastered a bit (old-school style like!). AMX Mod is now always maintained and finally purpose more than a half thousand mile of custom plugins, modern then properly and highly updated for the last versions (features).