nLab is a wiki-lab of a novel kind, for collaborative work on mathematics, physics, and philosophy, including original research, with a focus on (higher) category theory. The nLab espouses the n-point of view (nPOV): that category theory and higher category theory provide a useful unifying viewpoint for mathematics, physics and philosophy. The nLab was originally conceived to provide a repository for ideas (and even new research) generated in the comments on posts at the n-category cafe, a group blog run (at the time) by John Baez, David Corfield and Urs Schreiber. It has since grown to include whole research projects and encyclopedic material.
It is one of two wikis mentioned by the mathematical physicist John Baez in his recent review of math blogs in the Notices of the American Mathematical Society. Baez is the author of the earliest mathematical physics blog, which has run since January 1993.
The nLab is listed[1] on MathOverflow as a standard online mathematics reference to check before asking questions. Many questions link to the nLab for background material[2].
The nLab has an informal 'steering committee', which "doesn't run the nLab", but only exists in order to resolve issues that would cause the whole project to run into trouble. The steering committee operates mainly from the nForum, which also serves as a central hub for recent changes and the discussions attached to them.