Took me a while to figure out it was a fork of Ubuntu. Does System76 maintain its own aptitude repos? What custom software does it come with (if any)? What arch

Took me a while to figure out it was a fork of Ubuntu. Does System76 maintain its own aptitude repos? What custom software does it come with (if any)? What architectures does it support? What is the default desktop environment? There's no detail anywhere. No screenshots either.