MJOLNIR (not to be confused with Thor's hammer) is a gameplay mod that imitate Halo's gameplay meaning you'll only be able to have two weapons at once but will be granted more ammo, a regenerating shield, and grenades.
First release of MJOLNIR, more has to come, there's no alternative to the Rocket Launcher yet as the other weapons (Shotgun + SuperShotgun / Pistol ...