Below 2.6L as far as I remember the only options would be the old IDI BMW 2.4L/2.5L TD and "TDS" engines, and the VW/Audi 2.4L diesels as found in old LT trucks, Pinzgauers, and Volvos. There might have been a few of each technically made this century, since I think the BMW TDS engines were still around at least through the late 90s and maybe into the early '00s, and the VW/Volvo 2.4 TD was used in military applications that probably were still getting them past the turn of the century even as antiquated as they were (similar to Humvees here getting the old boat anchor IDI GM 6.5 well into the 2000s long after the consumer market had moved on).
But, even if a few of the above motors may have been produced this century they certainly were designed in the previous century and mostly use diesel technology from the bad old days -- mechanical pumps, prechambers, troublesome fiber headgaskets. I don't think that's what you have in mind.
3.0L you have the M-B OM606 and the BMW M57, and I think that's it. Maybe Opel or VM Motori made something too?
I always have thought it was a shame that when VW/Audi introduced TDI tech to their line of diesels in the '90s, the old mechanical 4cyl and 5cyl diesel families got revamed into electronic TDI engines but the closely related inline six version did not. In the same way the short deck 1.6TD, 400cc per cylinder wound up as the tall deck 500cc per cylinder 1.9/2.0 TDI, and the short deck 2.0TD 5-cylinder grew into the 2.5 TDI five, the 2.4L TD inline six would have ended up as a 3.0L TDI 12-valve inline six. Like a half-size Cummins. If HP levels tracked with the other engines using the modular TDI design, it might have had ~175hp and ~300 lb-ft from the factory, early TDI reliability, and I6 smoothness and sound. Wouldn't have taken hardly anything to do it, just a taller deck, new head design, and six of the same larger bore TDI pistons that were already being used in the I5.
I presume the reason it didn't happen is there was no application in VW's line for such a motor and Volvo was phasing out its RWD platforms too. Fun to imagine what it would have been like though.