Mechanism changes
Unimatics were an all-in-one, beltless, direct-drive mechanism that Frigidaire used in their home line automatic, solid-tub washers up until 1958.
Pulsamatics were a shorter-lived, belt driven mechanism that were, for a while, offered concurrently with the Unimatics on lower lines of Frigidaires. Their pulsation was really fast (630 PPM?), but their spin speed matched it (630 RPM as well), so they weren't as good (per se) as the Unimatic, which had a slower pulsation rate, but a wildly fast 1140 RPM spin speed. Also, the superfast pulsation, though dramatic, didn't roll clothes as well.
Multimatics followed the demise of the Unimatic, and though a good mechanism by definition, they are sometimes referred to as "Multitragic", among other reasons, because of a design where two belts drove the mechanism, and they're very difficult to tighten evenly for correct performance.
Rollermatic transmissions differed greatly from the transmission-case design of the Uni/Pulsa/Multimatics, because a series of interconnecting rollers passed power around to achive the pulsation/spin. These were used in the mid-to-late sixties solid-tub machines, and evolved into the "modified Rollermatic" 1-18 (which has a similar setup, but a drive belt as well).
I know the Frigidaire gurus are hammering away at their keyboards right now, and will correct the errata that I've presented above

But that gives you a very brief overview.