With the introduction of a subscription-based service, Viveport is becoming increasingly attractive to all VR users, including those with an Oculus Rift. The traditional model of buying an app once and keeping it forever is still supported, but you can now choose five VR titles per month to play for one baseline price.
Viveport is designed for use with the HTC Vive, but that doesn't mean the Rift is completely excluded; you can get it working with Viveport, but there are some drawbacks. Controls designed for the Vive wands can be a bit tricky to deal with, and apparently, some apps will simply refuse to work with the Rift (like Firebird - La Peri). It's hard to say exactly which games will play nice with the Rift, so tread carefully before deciding to spend your money.
That doesn't mean there isn't a ton of cool stuff in Viveport, both free and paid, for you to check out. Let's get it working with your Oculus Rift.