The M+ OUTLINE FONTS are a font family under the Free license. You can use, copy, and distribute it, with or without modification, either commercially and noncommercially.

Anonymous Pro is a family of four fixed-width fonts designed especially with coding in mind. Characters that could be mistaken for one another (O, 0, I, l, 1, etc.) have distinct shapes to make them easier to tell apart in the context of source code.

Anonymous Pro also features an international, Unicode-based character set, with support for most Western and European Latin-based languages, Greek, and Cyrillic. It also includes special "box drawing" characters for those who need them

The Liberation(tm) Fonts is a font family which aims at metric compatibility with Arial, Times New Roman, and Courier New. It is sponsored by Red Hat

Over at The Font Feed, one font-obsessed writer added up the  Top Ten Typefaces Used by Book Design Winners–an practical list of popular book fonts (and some alternatives). We’ve listed the top five below, complete with links to samples of each font. If you want more, explore the Quora thread about the topic