Open source mathematics 

Software:

• listing of some open source math software
• SAGE
• GAP (and partial mirror)  
• LaTeXML
• OpenMath
• OMDoc
• mathbuntu

Texts:

• planet math
• polymath blog,
• Wikipedia's list of mathematical topics,
• Open source math books on this site
• math bookshelf at project gutenberg   (public domain texts)
• math at the wikiuniversity

Papers:

• Math Preprints (arXivs)
• Electronic Library of Math (ELibM)
• online theses in number theory
• online theses database. It also has some full text
• plos.org, the Public Library Of Science (no math journals yet)
• Directory of Open Access (Math) Journals

General open education/knowledge links:

• The Open Knowledge Definition
  
• open source definition
• Open textbooks
• public domain texts at archive.org
• Open Educational Resources site has a math and statistics section (see also their textbooks section), with widely varying levels.
• Connexions