Kinda basic for the price, and the built-in store is the B&N Store. But they at least have EPUB and PDF support, and Adobe DRM compatibility, so you can hook them up to a PC and transfer books.

They do run a stripped down Android underneath, so you might be able to Root them and install a third-party launcher and apps on it, I’ve done this in the past, but I haven’t kept up in recent years(I’ve switched to Boox devices) so it might not be as easy to Root these days.