Are game modes in Garry's Mod free?

Do you have to pay for the gamemodes in Garry's Mod or are they free? I've looked up and not found anything and watched videos to try and find out but I did find a Steam page that some people say its free some say that you have to pay so are they free?

Solution 1:

All of the game modes in Garry's Mod are free. However, some servers or custom game modes may use assets from other Source games, such as Counter-Strike: Source, Team Fortress 2, or Half Life 2: Episode 2.

If you do not own these games or do not have them installed, any missing textures from those games will replaced by a pink checkerboard while missing models will display as a red ERROR.