Graphics Engines?

I have been noticing that in Emulators (Consoles on the Comp) use different graphics engines. EG: 2x SAL mode, Kreed's SUPEREAGLE mode. I've used them and they make the graphics looked softer and smoother without dipping the framerate? Are there C-Made DLLs like Supereagle.DLL or something to reproduce this effect?

TIA!
(Thanx in Advance)