The Alias mod is a plugin created by Fraeven and Rowedahelicon, it allows players to set a custom alias when connected to an SCG server that is different from their Steam name. Additionally, players can choose to have the SCG tag {SCG} affixed to their name / alias. It can be found on all Source servers, such as the Open Fortress or Team Fortress 2 servers.
Players can set their alias with the /alias "name" command. Players can then also toggle the alias being used, or their SCG tag setting, by selecting the relevant options in their client settings menu by using /settings. Players can also edit their alias / settings on the TF2 settings page on the SCG website.