Mizar Project  
   An attempt to reconstruct mathematical vernacular into a formal language which can be read by humans and also verified by software.
   http://www.mizar.org/

QED Project  
   Build a single, distributed, computerized repository that rigorously represents all important, established mathematical knowledge
   http://www-unix.mcs.anl.gov/qed/

Practical Foundations of Mathematics  
   Online text of the book by Paul Taylor, together with supporting materials. The text aims to provide a conceptual and formal foundation for mathematics and computer science.
   http://www.dcs.qmw.ac.uk/~pt/Practical_Foundations/

A Century of Controversy over the Foundations of Mathematics  
   Edited transcript of a lecture by Gregory Chaitin, author of `The Unknowable'.
   http://www.umcs.maine.edu/~chaitin/lowell.html

Arché  
   The Arche project looks at the foundations of mathematics, especially at Frege's Theorem and its ramifications. Based at the University of St Andrews.
   http://www.st-and.ac.uk/academic/philosophy/arche/

FOM  
   A closed, moderated, e-mail list for discussing Foundations of Mathematics moderated by Martin Davis. Archive available.
   http://www.cs.nyu.edu/mailman/listinfo/fom/

Foundations of Mathematics  
   This is a site for studying foundations of mathematics, or it can be used as a reference material. The site is structured as contents pages of a book on the subject of mathematics foundations. It comprises links to expository materials.
   http://sakharov.net/foundation.html