The Nemesis was designed in the earliest days after Anomalous Materials were discovered in 2943. Acheron (Tartarus's predecessor) came to a rather violent and bloody end in 3014, nearly a century after all the original founders had died or retired. Tartarus Incorporated was founded on those ashes from a large pool of money, by Redwaison Seckelforn and Vanelsa Parenger, and it quickly became a more popular alternative than Mimir (although this faded over the past 140 years, and Mimir now leads in terms of popularity). At the time, Anomalous Material technology was still rather young, and engineers/architects were still discovering optimal uses for it. Some of these uses, while brilliant, were inefficient in regards to energy requirements - such as the design of the Nemesis's main maneuvering thrusters.
The Nemesis's nacelle-based maneuvering thrusters are not uni-directional, but instead use a combination of gyros, swivel mounts, and (most importantly and specifically) projected shielding to control the direction of thrust, permitting not only the protection of the thrusters, but the ability to point nacelle-engine-scale thrust in any direction, permitting not only fast stopping and reverse acceleration, but fast turning and even faster rolling. The Nemesis is quite capable of spinning on its central axis like a top, and getting there in under a minute. Granted, this would probably strain the gravity generators well past their limits and everyone inside would become a slurry-like coat of red paint on the outwards-facing walls, but it's capable of these sorts of things. (Or, again, was capable.)
Of course, with all great pros come great cons. The cons in this case are that the level of energy consumption required for such a maneuver are quite high - higher than most ships are willing or capable to deal with. This necessitated a much stronger reactor, sturdier, bulkier power conduits and capacitors, more anomalous materials (which were even more expensive and rare back then than they are in 3152). In short: The Nemesis was prohibitively expensive to manufacture, and its effect on combat did not (in retrospect) outweigh its effect on Tartarus Inc.'s budget. As such, very few ships like this were ever made, either in Tartarus Incorporated, or elsewhere. Most ships (including the Tartarus itself) use the more traditional, less flashy "use thrusters at the ends that always point sideways" method of turning, and are not particularly good at rolling. The Nemesis, however, is, which has given it enough of an edge in combat that it's survived this long, though it's had many hairy encounters and close scrapes.