Accrescent is by their own team, I don't work on it. We have now chosen to add the option to install on our Apps app. They are maintained by long-time GrapheneOS community members and it's been designed for GrapheneOS users. We have been aware of the app for a few years.
https://github.com/accrescent/accrescent
It was always in our interests to have a more secure app store option as we didn't want F-Droid. Users are still free to install another app store of choice as Accrescent isn't and won't be bundled into GrapheneOS itself.