Groups comparison
Steamworks API - 2003 to 2020
The software part that ties a game to the Steam community, matchmaking and other features.
Valve Anti-Cheat (VAC) - 2004 to 2016
Steam Trading - 2007 to 2013
Supports Steam Trading which allows players to trade in-game items and such between players ignoring game boundaries in terms of what is tradeable for what (though usability is still likely restricted to the particular games).
Steam Workshop - 2007 to 2017
A distribution system for user-created content on Steam.
The software part that ties a game to the Steam community, matchmaking and other features.
Valve Anti-Cheat (VAC) - 2004 to 2016
Steam Trading - 2007 to 2013
Supports Steam Trading which allows players to trade in-game items and such between players ignoring game boundaries in terms of what is tradeable for what (though usability is still likely restricted to the particular games).
Steam Workshop - 2007 to 2017
A distribution system for user-created content on Steam.
steamworks
valveanticheat
steamtrading
steamworkshop