64 x 44, monochrome. Screenshot taken with the EightyOne emulator.
I was wondering if there was a machine with more primitive graphics than the TRS-80, and then I remembered the Timex-Sinclair 1000. I sort of wish I hadn't.
Known in the exotic foreign land of its birth as the Sinclair ZX-81, it was a bit of a technical marvel: A functional home computer with a working version of BASIC that retailed for only $99 USD. Unfortunately, they got there by cutting every corner available. Tiny, scrunched together membrane keys, video was shared with main memory (and moved around as you programmed!), tape cassette storage only, and slow as molasses. I spent several evenings trying to get my little pixel plotting program to work, and then several more making the picture, since it took about 1.5 seconds to plot or move each time.
I'm totally not using lo-res formats to hide my lack of artistic ability. I mean, look at that tree!