Directories

Alternative OSs on the Net
A list of operating systems and OS link sites.
http://www.d1.dion.ne.jp/~r_high/GeekOS/indexos.html

A Catalog of Operating Systems
Classified, alphabetic listing of most operating systems, past and present, distributed commercially or reported in English-language literature, platform oriented. From Computer Science 258, West Virginia University.
http://www.csee.wvu.edu/~jdm/classes/cs258/OScat

Microcomputer Operating Systems
Some 70 OSs that run on microcomputers, PCs. User interfaces in earlier systems are command-line, character-oriented; later systems are mostly GUI-based. List, with brief descriptions, no links. From West Virginia University.
http://www.csee.wvu.edu/~jdm/classes/cs258/OScat/micros.html

Open Source Ring
Alphabetized list of many links, OSs, projects.
http://www.webring.com/hub?ring=os

Paul Hsieh OS Page
Loosely categorized list of about 100 links to developer resources for creating OSs, emulators, alternative OSs.
http://www.azillionmonkeys.com/qed/os.html