Original thread is here: http://forums.sonicretro.org/index.php?showtopic=15178 Would've posted in that, but it appears to be locked. It seems unfortunate that it was hosted on sepwich.com which got killed earlier in the year, and Google reveals no alternative links at all, a couple of project sites mention it but attempt to link to the now defunct download address. Did anyone download this back then and keep a copy of it, because it seems this Shibunoa/Tails92 guy is very difficult to get? Thanks.
Coincidentally, I found the equivalent of this program just a few days back. I can't remember where I found it, but I think I found it at Eidolon's Inn. It's called STMView. It's not exactly the same as SCDPlay, but it will read the .stm files from Sonic CD AND Ecco the Dolphin! I'm not sure which is better/newer, but for now just use this. If you can't find it there, just PM me, and I'll send you my copy.
Found a copy of SCDPlay on my hard drive. I think this should be the last version. http://www.mediafire.com/?yt62u64d8xb62w6 Who wants to add this to the wiki?
I'm considering writing my own version of the tool based on the viewer code in the actual Sonic CD assembly. I'm tinkering here and there with my disassembly again, but don't expect anything announcement-worthy for a while.