These are all at various stages of production/usability:
Most of the people here just use emacs/vim/etc. and then use the built-in webserver for simple stuff. (see http://wiki.freeswitch.org/wiki/Webapi)

For the others:
WikiPBX is an enigma. I haven't heard of anything new in quite some time. I don't recommend it.
FreePBX V3 - very promising, in early development, don't expect anything usable right away
FusionPBX - Farther along, simpler than FreePBX, closest to being usable in production
FSGUI - Donated to contrib by jmesquita; simple, work in progress, interesting to play with

CudaTel - It's the bomb! ;)

-MC