The perception of 'new' is maybe an individual one as...
Recalling the rise of 16bit era, defined mainly by Motorola 68k cpu computers
When ignoring the TI 99/4 (and PC (*1)) that is.
The Mac, brought the GUI interface.
Not really. It was already on sale since 1981 by Xerox (and others) (*2) as well as offered in form of the Apple Lisa, which wasn't so much more expensive as the mac. Consider that, at the time when the Mac came with a single drive and 128 KiB at 2500 USD, the Lisa 2/5 was sold with four times the memory (wich was pricey at the time), larger screen and 5 MiB hard disk for 5000 USD - dropping even further with the MacXL.
The A bomb,
the Amiga, with its custom chips-coprocessors,
Which is essentially just a souped (*3) up Atari 800 chipset (*4), so nothing basically new here (*5).
See Atari 800.
See Apple II sound cards, like the Mockingboard A of 1983 (*6).
pre-emptive multitasking OS
Many computers had that already decades before, not to mention MP/M for standard S100 boxes. Oh, and for the home computer segment for sure the Sinclair QL, did beat the Amiga not only by time but in quality as well (*7).
Having that out of the way, the Amiga OS did in fact set a true first by being the first Multimedia OS outside research (*8). Amiga OS did not only allow to play multimedia, but moved it from a special (application) mode into a generic feature with seamless integration, and right into mainstream. A feature others, like Windows, BeOS or MacOS, only gained more than a decade later.
That's a first that'll stand the test of time.
and probably other stuff which I forget.
I'd have a hard time to come up with any other.
And also Atari ST. Well, it had midi ports embedded, making it successful among musicians. I also remember its crisp 70Hz 640x400 monochrome monitor, very easy for the eyes, paired with a nice, legible 8x16 font. But did it bring any novelty, like the aformentioned two (Amiga, Mac)?
Now, if you consider any of the above parts (GUI, Graphics) as new, then the Atari's screen mode was for sure revolutionary. While such screens were known with professional system, it was a first on the "affordable" price segment.
I'd say, the 'new' in the all examples mentioned is the affordable part. Scaling existing features to enable a mass market.
PS: I also remember IBM PC with its 8/16bit 8088 cpu as a lousy machine with only one nice feature: Its expansion slots!
A feature IBM copied from the Apple II - which can be considered in many details the blueprint for big blue's PC :))
*1 - Yes, the 8088 is for all context a 16 bit system. Bus width is about the least significant factor, or would you consider a 68030 working on an 8 bit bus (which it can without additional logic by simply tying DTACK0/1) an 8 bit CPU? The 8088 is a smart choice, as it's only 25-30% slower than a 8086 at the same speed, but saving on components.
*2 - Sold in considerable numbers as 8010 since 1981, as well as several thousand by Siemens as EMS 5800 since 1982. Heck, there is even one to be see within Commodore's Amiga department- the large screen in the corner.
*3 - After all it was designed by the same team as the preceding Atari chipset - and intended to become an Atari machine.
*4 - ANTIC, C/GTIA and POKEY became Angus, Denise and Paula, maintaining essentially the same organisation of
- DMA/Address Ggeneration (ANTIC/Agnus)
- Video generation (GTIA/Denise)
- Audio/Joysticks/Serial and other I/O (POKEY/Paula)
*5 - In fact, there were tricks the Atari Chipset could do (at lower resloution), impossible for the Amiga - like anything charset related.
*6 - The board used/shown is a 1:1 modern replica. only difference is a standard stereo connector.
*7 - Using multitasking on the Amiga was comparable clumsy and error prone, while the QL could do it with a few lines in BASIC.
*8 -That is outside specific applications, supported by add on hardware. All the elements from DMA for video generation all the way to Genlock have been made as early as the first bitmap video cards for micros.