This gamemode is a non-serious role-play gamemode, where players often build large bases to protect themselves and various entities that can produce money. Players are often given the means to “raid” other players by breaking into their homes/bases and either stealing or destroying valuable entities. This gamemode features jobs (or roles) such as police, gangsters, citizens, and gun dealers (a kind of merchant), and is arguably the most popular gamemode of Garry’s Mod to date.
Military RP is a serious role play gamemode in which the player takes on the roll of an enlisted military serviceman/woman. This kind of role play is very strict, requiring players to follow an extensive set of rules. Players will typically obey the orders of other players with a higher “rank” than them, emulating a military hierarchy.
Star Wars RP
Star Wars RP is a collection of different Star Wars themed Military RP gamemodes, usually set in various arcs of the Star Wars canon. They became popular in late 2015 when Star Wars Episode 7 came out in theaters. The most common arc for these kinds of gamemodes is the Clone Wars era, and players will take on the role of a clone fighting droids/sith/etc. Virtually identical to the Military RP gamemode, except Star Wars.
There are a lot more but these are some of the most popular and my favorite.