fictionbook.org - portal dedicated to fictionbook format. Explains xml structure of the format, specifications. Contains also information about readers, editors, converters and librarians that are able to work with fictionbook format.
fictionbook.ru - russian site which contains a lot of fictionbook eBooks in russian language.
Project Gutenberg - a huge collection of digitized books mainly in plain text format. Founded in 1971 by Michael S. Hart, it is the oldest digital library.
Haali Reader - eBook reader capable of reading fictionbook format (for Windows Mobile).
FBReader - eBook reader capable of reading fictionbook format (for many different platforms including Linux, MacOS, FreeBSD, Maemo, Google Android, Windows XP ...).
jFBLibrary - Software for archiving, classification, collection and search of FB2 electronic books. Written in Java, it supports Linux, Windows, MacOS and other systems capable of running JRE 5.0 an higher.
Calibre - a free and open source e-book library management application running on Linux, OS X and Windows.
ZXReader - a free e-book reader for Symbian mobile devices.
launchpad.net/acbf - Advanced Comic Book Format (ACBF) project pages. Contains the specifications documents, XML schema, ACBF Viewer downloads for Linux and Windows and its source code.