"Categories of Free and Nonfree Software" is a maintained reference document in which stallman provides precise definitions for the major categories of software distinguished by their licensing terms and freedom properties. It is a taxonomic companion to the free-software-definition and the free-software-definition-essay, providing the vocabulary needed to discuss different software types with precision.
The document defines: free software (satisfies all four-freedoms); copylefted software (free software under a license like gpl-v2 that requires derivative works to be free); noncopylefted free software (free software under permissive licenses like MIT or BSD that permit proprietary derivatives); GPL-covered software (specifically licensed under the GNU GPL); the GNU system and GNU/Linux (see gnu-linux-naming); open source software (a category stallman regards as overlapping substantially but not completely with free software — see software-freedom-vs-open-source); public domain software (no copyright, therefore free but also unprotected against appropriation); freeware (nonfree software distributed at no charge — distinct from free software); shareware (nonfree software distributed for a trial period); private software (not distributed outside an organization); and proprietary software (distributed but under restrictions).
The distinctions matter for stallman's political project. The term "freeware" is particularly important: stallman insists it should not be confused with "free software" because freeware is typically proprietary software distributed at no cost, satisfying none of the four-freedoms. The libre-vs-gratis distinction underpins the entire taxonomy.
The document also clarifies the relationship between copyleft and the broader category of free software. Not all free software uses copyleft; some free software uses permissive licenses. stallman regards both as genuinely free, but he prefers copyleft for the strategic reasons articulated in copyleft-pragmatic-idealism and why-copyleft.
The document is updated as new categories become relevant — for instance, the document addresses cloud software in later versions, connecting to the saas-loophole problem discussed in who-does-that-server-really-serve.