The Razorback was developed after the Horus Heresy, and was intended to provide Space Marines with heavier fire-support. In contrast to the Rhino the Razorback loses its firing points and can only carry 6 Space Marines, but in return it gains a variety of heavy weapon options. This enhanced weapon mix means that the Razorback is a very flexible way to get more firepower on the table while still providing transport capability.
The Grey Knights are known to make use of their own unique variant of the Razorback known as the Vortimer Pattern. Armed with a set of twin-linked psycannons, only about a dozen are left in the chapter's armory, meaning that every deployment of these venerable vehicles must be approved beforehand by the chapter council.
The Chaos Space Marines were intrigued by the design of the Razorback after encountering it, but ultimately decided to simply arm their Rhinos with support weapons instead, since that didn't involve flagging down manufacturing plants (of which they don't have anywhere near as much as the loyalists) or cutting the transport capacity by 40%. As such, the Razorback remains unique to the Space Marines, aside from the occasional stolen or looted vehicle. Primaris Marines get their own flying Razorback.