maybe a bulletin board, again in university's mathematics department buildings.
people post proofs they write in the board, others post commentaries, correct mistakes, point out different proofs to the same proposition, etc. actually, the interaction seems endless to me.
@Roland yeah, i have to find people, actually writing proofs :)
and i impose tex typeset document, on top of that. ugh, i won't heal, i know. :)
it's so alluring to dream of though :)
"I appreciate SDF but it's a general-purpose server and the name doesn't make it obvious that it's about art." - Eugen Rochko