The Lionheart/DP-51/DH-40 are the ONLY pistols I've heard of or handled that had this interesting (tri-action) trigger. I think LH has a different name for it -- but as best I can tell, it works the same.
For those unfamiliar with the design, it has three modes: 1) standard DA start. 2) standard SA start (cocked and locked), and 3) a hybrid SA mode in which you manually cock the hammer, and flip it forward -- but you need not set the safety..
While this sounds dangerous, it isn't. There is takeup in this 3rd mode, which flips the hammer hammer back -- and it is clearly felt in your hand (and trigger finger), very easy to control, and then a bit like the standard SA mode, but less noticeably trigger action than DA. The safety can be engaged in any of the three modes if it's a concern to the shooter.
I've bought, traded, and sold a lot of guns over the years and (when I didn't sell for financial need), of those guns, the only ones I really regret selling were my first DP-51 and a CZ-40B. Mags were sometime a problem, but the S&W 59 series mags worked in the 9mm (and could be made to work in the .40 version), and stuck out maybe an 1/8" more than stock mags. I suspect you can get mags now (at least for the 9mm) from Lionheart.