Nonworking hosts have been removed (which was most of them). Uploads now happen over https. There is early support for hosts that require authentication keys (currently only sicp.me) and the looks have been updated.
On a more technical level, the app has been rewritten in Kotlin, uses more recent dependencies and Android recommended practices. As a consequence, support for very old versions of Android has been dropped, but it should still work on Android KitKat (4.4) and later.