Recs.
Updated
Hack is a typeface designed specifically for source code, an evolution/synthesis of two older programming-focused fonts: Bitstream Vera and DejaVu. Intentionally crafted with a rendering sweet spot between 8-14px and sparing use of serifs to aid in distinguishing the most commonly confused glyphs, it's developed as an open source project.
SpecsUpdate
Pros
Pro Libre webfonts are available in svg, eot, ttf, woff, and woff2 formats
Hack is free for unlimited commercial and non-commercial use. The webfonts are hinted (TrueType instruction set) to optimize display on the screen and are built into all commonly used web font formats with each new release. They include the complete release character set and smaller (filesize) basic Latin subset releases. They are available in the build directory of the repository.
Pro Fixes many readability issues in Vera/DejaVu
The tilde symbol ('~'), comma (',') and semicolon (';') glyphs have been modified to be more readable at small sizes and/or on non-HD displays. In addition, the underscore symbol ('_') has been slightly lifted for alignment with surrounding characters.
Pro Good support for combining characters/diacritical marks & fullwidth characters
In terminal emulators that don't automatically correct for this (Alacritty), many monospace fonts will display combining characters and diacritics incorrectly, appearing offset from the base character by as much as an entire column. Additionally, some fonts will not properly handle fullwidth characters, causing them to overlap the following character. This font handles both well, fullwidth characters are properly spaced and combining characters render at their appropriate locations.
Pro Based on the tried and tested Bitstream Vera Sans Mono
The fonts are in the Vera Sans Mono lineage with a significant expansion of the character set (which includes Cyrillic and modern Greek character sets), new glyph shapes and modifications of the original glyph shapes, as well as improvements in metrics and hinting/TT instructions to make it more legible at small text sizes used for source code.
The changelog is available here.
Cons
Con Sometimes difficult to distinguish lowercase "i" and lowercase "l"
When using a higher resolution monitor and a smaller font size, the lowercase "i" and lowercase "l" are very difficult to distinguish. The space between the dot and the remainder of the letter seems to somehow disappear, thereby making it look like a solid line, similar to the lowercase "l". Yet on regular DPI screens it looks perfect.
Recommendations
Comments
Flagged Pros + Cons
Pro Powerline glyph patch is included
The regular set is patched with Powerline glyphs by default. There is no need to patch the font to use it in Powerline environments.