Essentially, it's GNOME. The shell is phosh instead of the GNOME Shell, but you can see from the video that the look and feel is intended to match GNOME Shell.

The default apps will be GNOME apps. You should be able to run other Linux apps just as easily, assuming they fit the touchscreen and CPU architecture.

GObject have bindings for virtually every language. (gobject bindings can mostly be autogenerated so it will be easy to provide bindings for librem specific libraries too)

> Will developers be expected to write their apps in C/GObject?

I think this will be the "default" and it's the thing I'm mostly excited about. I've been prototyping an app and it's a small simple c file, the android equivalent would be dozens of xml files and require an IDE.

There are a lot of bindings for gtk though, and they do like to push their xml gui builder abomination.

I imagine you'll be able to write apps in Qt/QML[1], which already provides a UI optimised for a phone[2].

[1] Available in Debian, and therefore by extension, PureOS [2] SailfishOS, the other mobile Linux OS, uses Qt/QML for its apps