Little known to most people, is their YS mount lenses (similar to the Tamron Adaptall mount). The Y in YS stands for Yamaki, as in Yamaki System. Though the mount was short-lived and not particularly successful, it was one of the few interchangeable mounts that competed with Tamron interchangeable mount.
Of course, Sigma was the only manufacturer who tirelessly pushes (and most likely not making much money from) the X3 Foveon (now Sigma) sensor, and was the first to introduced a pocketable digital camera with an APS-C sized sensor. They have my respect for trying so hard to make a difference in the camera business where everyone else uses a Bayer sensor.
Rest In Peace, Mr. Yamaki. Thank you for all the nice lenses and cameras you have made (and will make).
Sigma YS Mount 55mm f2.8 Macro & Canon T2i. Click for larger size.