I've been debating with myself over covering this one as "obscure", because it actually does appear to have a bit of a following, however, that following seems to be somewhat niche (chiptune folks), so I think it qualifies. I'm not a big chiptune enthusiast myself, though I have a passing interest. I am, however, interested in synths of all sorts, and as a child of that era, I do have a bit of a fascination with the old soundchips. DefleMask is available for Windows, Mac OS, and Linux.
Behind the mask
I won't go into detail about every feature here, but here's a basic rundown: DefleMask has full real-time emulation of a bunch of these old soundchips, eight as of this writing, including most things I imagine you'd want from a chiptune synth. It includes instrument editors for all systems, and can can even build ROMS for all supported systems, so you can play anything you make on the actual hardware.
As far as the synthesis goes, I can't really comment with any authority on the quality of emulation as compared to the actual hardware, since I don't have access to any of the systems in question. However, they all sound good to me in a basic sense, and also as an old guy who has at least heard all of them at some point.
For the most part, it's easy enough to navigate, though the tracker interface may put some off these days. It does support MIDI input though, and includes an editor for keyboard shortcuts, which may help make it more comfortable.
Put it on
There are certainly other ways to get retro-style sounds, arguably easier ones, if trackers aren't your thing. For many who aren't making chiptunes, having a really good emulation of some specific chip may not be important. However, I find it fun to play with, and figured at least a few others might too.
Website: http://www.deflemask.com/
Thanks for checking out this edition of Obscure Audio Software! Feel free to comment below, either about this article or DefleMask itself, or something else you think would make a good subject for a future edition of Obscure Audio Software.