If you are an emacs user, you might be interested in org-drill, which of course is plain text and uses space repetition algorithm:

https://orgmode.org/worg/org-contrib/org-drill.html

org-drill has not been maintained in a long time. I would recommend org-srs[1], which admittedly may also one day not be maintained (single developer curse). However, I think it has some benefits over org-drill, the main one being it supports FSRS.

[1] https://github.com/bohonghuang/org-srs