The original host of the files (opensa.dantarion.com) is currently down. This exists to provide an additional host in case other sources go down.
Also please read the following from ToomaiGlittershine (https://old.reddit.com/r/smashbros/comments/17b1i37/im_looking_for_opensa2_brawl_modding_tool/k5j80fe/):
So opensa.dantarion.com is finally dead, eh? That sucks, but at least the wiki part is still partly archived (if maybe fully, haven't scoured around).
I have OpenSA2. The problem is coded kinda weird (and dangerously!) in that it doesn't download itself to a sensible location, instead burying itself in your AppData files. Luckily, the task manager menu let me track it down.