This doesn’t add anything to the post, so, sorry, but this is a really good question! Thanks for contributing!

I don’t know it it’s underused, but my go to for years gas been League Spartan from The League of Moveable Type

For those who love comic sans I might have bad news: you might be borderline dyslexic.

Switching to OpenDyslexic 3 helps

Agave. My favorite monospace/programming font. What I like best about it is how the baseline isn’t where the descenders begin. Makes it look unique in a nice way.

I really like Open Sans

I’d say several fonts on Google Fonts (the only place I know lol) are pretty good. I don’t see them mentioned anywhere and I’m not a font enthusiast per se, so I’d call them less known. Some of my favourite - Courier Pro, Doto, Sono, SUSE Mono, Josefin Slab, and Martian Mono.

And a couple others default on my Windows PC that I like: Bookman Old Style, Yu Gothic (Fun fact - this font was used by the hit anime Neon Genesis Evangelion for their english title cards) and wierdly enough, Segoe UI. I love that Windows 8 aesthetic it brought.

Shout out to 0xProto! Texture healing in a monospaced font is super cool!

I love this hyperlegible one from the Braille Institute: https://www.brailleinstitute.org/freefont/

There are too many to mention since there’s so much out there.

You can go to a font website like dafont and perform a search for a font or browse different themes/styles and specify in the results that you want Public domain / GPL / OFL fonts.

Almost all of my fonts are released under an attribution license, so they’re free for commercial use and remixing.

https://michaelwmoss.com/typefaces

M+ 1m has been my daily monospaced font ever since I found it, which is about eight years now. I don’t see it come up often when people talk about monospaced fonts.

Comic sans.

Ärzte Sans (edit: missed the open source part. I can’t verify that)