Student or Learner
Imitated or simulated dresses
The dresses of famous designers but with a cheaper price.
Also imitated or simulated computer programs
The countefeits are imitations, not simulations.
We use knock-off in BrE too.
Pirate is also used for software.
Just a semantic note here: For pirating software, I wouldn't put it on the same level as an imitation or knock-off (which can be a synonym for generic.) In most cases it's having the actual software...just without paying for it.
Microsoft have a piracy page, and in it they do break it down into counterfeit, unlicensed or pirated software, but in general terms, and as these things are on a sliding scale from copies, through cracks to fakes, I see pirate used in BrE as a general term for any dodgy software
You can also pirate movies and music.