Sweetmugen was created some time before 2009 however the exact date is not certain.
The website and warehouse was run by some french mugen creators that were well known during the early days of mugen dos and winmugen, but not so much now.
The administrators and moderators for the forum were: Mike Werewolf, Scal, Zesensei, & Cerisier.
Currently the forum is completely dead missing, but all of the images and database entries are intact.
You will find a lot of old content here and offsite links to some very old geocities japan mugen websites among other things.
If you are looking for a trip down mugen memory lane, this place is a good place to start.