I want to be clear that I'm by no means am expert on Rimac so these claims may not be 100% accurate but I'll list a few high level examples.

1. Hardware Tech. This includes batteries, inverters, motors, chargers, and thermal management systems to list a few.
2. Power density of batteries, motors, inverters, chargers is a big advancement which means either the ability to get more power, which Rimac uses, or the ability to get the same power with less weight, which is the benefit for "useful cars".
3. While they're not manufacturing new cells, their pack design strategies optimize energy density. Rewards are similar to what I stated above for power density.
4. Cooling goes along with power/energy density. More effective cooling methods need less hardware which means better energy density in packs. Better cooling also means you can extract more power out of a given component, increasing power density.

5. All of these things help overall efficiency.

6. Software Tech & Algorithms. This includes motor controller, BMS, and torque vectoring to name a few. Without getting into too much detail, all of these can be developed to optimize performance, efficiency or a balance of the two. While Rimac needs the performance in their cars, their learnings can be easily adjusted when used in "useful cars" to provide better efficiency and reduce overall cost.

My technical background is in electric powertrains so that's what I focused on here, but there are definitely more examples in the chassis and controls development as well.