When fretta stopped being supported by Facepunch, gmod updates eventually broke many original and fun games still using it as a base. fretta13 is an update of the abandoned fretta gamemode base for Garry's Mod. It's meant as a direct replacement for fretta. If anyone would like to update older, broken gamemodes still stuck using "fretta" as a base, the first step should be to point to fretta13 as the new base.