I forget who round here recently praised the JetBrains mono font, but reading this and seeing it's licensed as open source, I am tempted to try it out: https://www.jetbrains.com/lp/mono/
JetBrains Mono: A free and open source typeface for developers
Try JetBrains Mono in your IDE. Its simple forms and attention to every detail make coding a nice experience for developers’ eyes, no matter which IDE you choose.
JetBrains: Developer Tools for Professionals and Teams
Trying it out on #emacs, but I'm not instantly sold. I quite like the retro look of Courier New for code and I tend to find serifs improve readability. This has put the cat among the pigeons though, because I can't remember what the default font was previously...