AtlantisMUCK started in late may or early june of 1990, and was the first
programmable TinyMU*, running the TinyMUCK2.0 software.

CrossRoadsMUCK was a large project that had about a dozen people working on
building the ultimate puzzle/setting unthemed mud.  It started in Oct 1990,
and was under construction until about june 1991, when it opened.  It then
was open until december 1991, when it lost its site.  It had good building,
pioneered a lot of the common MUCK programs that are about nowadays, and
had several neat and complex puzzles.  Unfortunately it also ran on a slow
machine that didn't have a very good netlink, and it suffered from some
political disagreements among the wizards.

Second System Syndrome helpful stats:
TinyMUCK 2.2: 22,000 lines of C code.
TinyMUCK 2.2fb5.40: 39,000 lines of C code.