A well designed clear font will increase the readability of programming source code.
The fonts listed below are some open source alternatives to the default monospaced OS fonts (Courier, Consolas, Lucida Console, Monaco).
The ideal font will depend on your monitor size and DPI, font size and whether you use Font Smoothing or ClearType.
ClearType and the fonts hinted to use it (Calibri, Consolas), do not display well on tablet devices when rotated 90°.
Anonymous Pro by Mark Simonson - Full unicode and bitmap support.
Andale Mono - via Microsoft Core fonts.
Adobe Source Code Pro by Paul D. Hunt, (also the companion Source Serif Pro by Frank Grießhammer).
Bitstream Vera Sans Mono by Jim Lyles. A derivative of Vera Sans Mono, Menlo, is provided with Mac OS X. DejaVu fonts are also based on Vera.
Courier Prime - an updated version of Courier with true italics, designed primarily for screenplays.
IBM Plex Mono - Full font family with sans and serif by Mike Abbink and Paul van der Laan.
Droid Sans Mono - via the Google Andriod project.
Fira Code - A Monospaced Programming Font with Ligatures. Sponsored by Mozilla, (also the companion Fira Sans).
Inconsolata by Raph Levien, similar to Consolas but works equally well with ClearType on or off.
Monoid by Andreas Larsen, an example of Class Based Contextual Positioning.
Ubuntu Font - custom designed font with a very distinctive look and feel.
Input is a flexible system of fonts designed specifically for code by David Jonathan Ross. It offers both monospaced and proportional fonts, all with a large range of widths, weights, and styles for richer code formatting.
“The loveliest faces are to be seen by moonlight, when one sees half with the eye and half with the fancy” ~ Persian Proverb
Charter - A free body text / screen font font designed by Matthew Carter.
Google Noto - Open source unicode font, Noto Sans and Noto Serif support 581 languages.
Cooper Hewitt - A contemporary sans serif, by Chester Jenkins free for unrestricted public use under the SIL Open Font License.
iOS fonts - List of fonts supported in iOS