SuperMemo 7 available here is fully functional; however, you are legally limited by the licence granted to you for 1-month use.
This was the most popular Polish Windows product in the years 1993-1995!!! (as voted by readers of PC World Komputer).
Do not forget that from this site you can also download an excellent 40,000-item database for learning English (for SuperMemo 7)! You can also download a number of freeware databases.