This is a list of mono-spaced fonts, Unicode fonts, font resources in general and useful FLOSS font sites.
Monospaced fonts are particularly useful for programming. They can help improve readability. Some programming editors (like PFE) only work with monospaced fonts. Other editors allow the use of more varied fonts. However, monospaced fonts are useful when working with PRE tags in HTML, ASCII art and in other areas.
Other useful fonts include Unicode fonts for internationalized projects and fonts for people with handicaps or disabilities such as fonts designed for people with dyslexia.
Using a Free, Libre or Open Source font or a public domain or Creative Commons licensed font makes it easy to reuse fonts in Open Source (or even commercial) projects.