- Black Mesa - A total conversion mod of Half-Life 2 that features the original Half-Life storyline, characters, and enemies in the high-definition graphics of the Source engine.
- Dear Esther - An experimental "ghost story" created as a research project at the University of Portsmouth. It was released in 2008 as a free mod, and an updated 'Indie' version was released on a commercial scale via Steam on 02/14/2012.
- Eclipse - A fantasy themed action-adventure total conversion mod in 3rd person view, developed by students of The Guildhall at SMU.
- Received 2005 Editor's Choice (released mod) from Mod DB.
- Flipside - a mod where the player takes the role of a mental patient who is breaking out. Flipside was an IGF 2008 Finalist and received Mod DB's 2007 Editor's Choice award.
- MINERVA - Episodic single-player mod based in the Half-Life 2 universe, with a style of storytelling inspired by classic games such as Marathon and System Shock. The first chapter, Metastasis, consists of 4 episodes: Carcinogenesis (September 2005), Downhill Struggle (March 3, 2006), Depth Charge (October 1, 2007), and Pegasus (October 1, 2007). MINERVA was ranked #11 mod of 2005, #5 mod of 2006 and #5 mod of 2007 by Mod DB.
- Nightmare House 2 - This horror-themed mod was nominated at the ModDB 2010 Mod of the Year awards for Best Original Art, Best Singleplayer Mod and Player's Choice Mod of the Year categories, eventually winning 2nd place at the latter.
- 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. Gameplay is similar to Portal in its basic aspects: There are 19 Test Chambers in which puzzles must be solved in conjunction with a "portal device".
- Research and Development, a "non-combative" modification created by Matt Bortolino 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.
- Riot Act - A mod set in the universe of Half-Life 2. Players take on the role of Jamil Lee, a young member of the civilian resistance. She begins the game imprisoned at Nova Prospekt by the Combine.
- The Stanley Parable - An interactive fiction modification, with multiple endings depending on decisions made by the player.
- Weekday Warrior - A comic book mod developed by students of The Guildhall at SMU. It won Best Mod of the 2007 Independent Games Festival Mod Competition.
Read more about this topic: List Of Source Engine Mods