Mathematics for Web 2.0, Mathfuture Wiki.

#mathchat, a Twitter hashtag, by Maria Droujkova.
#mathmarkup, a twitter hashtag for LaTeX, MathML and related topics.

The social network, created by Rashmi Kathuria on the service.

The, discussion group Math, Math Education, Math Culture, created by Opher Liba.

The, discussion group Math Matters , created by Rebecca Hanson.
Wiki used for sharing diagrams to the above LinkedIn group

Orkut Mathematics (One), owner: Wat An Idea.

Orkut Mathematics (Two), moderators: Balakrishnan, Mihir, Hrishikesh, Ranajeet, Cláudio, Paramanand, NiLos.

Mathematics CyberBoard include equations that are entered as LaTeX and embedded as images within the text.

The Thesaurus of mathematical terms uses Java for graphics. Browsing the site with Firefox, it uses MathML for equations. Browsing with Internet Explorer, it requires the free MathPlayer plugin; as described on the the Help Page.