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No OS or onboard ROM- it's designed more after the NES than the C64

Currently the only controllers are gamepads with 8 buttons total, including directions. So text entry would be a bit challenging if it booted to a BASIC prompt. But apart from that it should be able to support a port of ehBASIC or something similar.

It doesn't yet have a BASIC cartridge but there's no reason it couldn't!

It would just need an adapter for the rear expansion port to plug in a keyboard, easiest would be PS/2 style like in the Ben Eater tutorials