Old olympus OM, original Nikon F* and contax-yashica CY mounts (see
here) all have similar or slightly longer registration distances than PK, and the bayonets are very similar in dimensions to PK which is why the "
multimount" works. The latter is in fact one of the two best ways of using eg a CY mount zeiss distagon on a pentax. The other is a custom
leitax mount swap. I've often thought it would be nice to try a classic "zuiko" or two on my K5, but basically getting it on would require a little judicious grinding/filing of the OM bayonet. But it might be worth it, the zuiko 50mm f1.8 is actually a much classier metal lens than the plasticky smc-a 50mm 1.7. DIY mount swapping is mainly not worth the effort, though there are cases where it might be eg a less common mirror lens - and I have a project on the back burner to look at converting my FD 400mm to PKA...
*Nikon F can often be squeezed on to Pk in any case. It's not very secure and the lens IME is usually upsidedown, but it works. Note that the later AI/AIS mounts have protruding connections that prevent any mounting on a K-mount.
T-mounts are a generic screw-on swappable mount, originally attributed to tamron but used by many manufacturers to this day. The mount does not allow aperture connections so lenses are typically preset, but that makes them cheap (my info page on t-mount isn't up for the mo after my bruv in law switched servers without telling me...).