I use runnerup from Fdroid. It can auto upload to runningahead.com ( which is on not foss but a passion project) which I like for getting weekly summaries and as a backup.

LA Times. Its free and has a good mix of synonyms, word play and trivia. Although I often only get the trivia (musicians, sports) courtesy of guessing after filling in a few perps, its a fun way to learn.

Thanks - but having to host NextCloud is a dealbreaker for me. It seems very exciting and perhaps I’ll learn how to do this at some point, but I’d really love a simple standalone program.