It may not be widely appreciated but UniPrint (or more accurately these days UniServer) does more than just printing. Many users find it invaluable for launching files and URLs to a PC when RISC OS can't handle them. And it has been, and will continue to be, regularly updated with new functionality, such as UniScan which was added recently.
I would also suggest that Grapevine is an important application - probably not used as universally as ArtWorks but there is no other app on the platform that does the same job.
Disclaimer: but then I would say that, wouldn't I?