https://render.com/ These folks are a production solution and have added support for review apps. All that happens is a new deploy of the production app on every PR. There's no support for spinning up arbitrary commits, caching, etc.. Further, its not free.
https://vercel.com/, https://www.netlify.com/ Only supports frontend (and maybe serverless?)
https://www.releaseapp.io/, https://getdockup.com/ These are both more direct competitors. Dockup is no longer around I believe. Wrt/ release we have different outlooks on pricing, as they charge a large initial fee. The product itself is similar, however.
And lastly, Heroku was discussed in threads below, but the general idea is that if you're already on Heroku, using review apps makes a lot of sense! With that being said, they don't support the features I mentioned above such as, restarting runs, comparing commits, caching, etc..
Let me know your thoughts, happy to keep the conversation going!