(This is a remake of the original Risk of Rain, out now)
Gearbox bought the franchise from its original devs about a year ago, and this is one of their attempts to capitalize on that purchase.
Hopoo, the original devs, were already making this and got to finish working on it after the purchase. It adds new content and refines the gameplay of the original (movement feels better and the game just generally plays better) - it was also designed with modding in mind.