There is Halo Spartan Assault, Halo Spartan Strike, Halo Online, Halo Zero (Fanmade), Halo 2.5 (Calling it another thing cus it's a whole lotta shebang) and another game which was 2D (Forgot the name)
Oh yeah Halo 5 is also there thru Windows Store.
Project Contingency is a WIP (I think it's dead)
EDIT: Halo Wars 2