I've been using google keep to take notes and remind myself to review them with spaced repetition (more about spaced repetition https://apps.ankiweb.net/docs/manual.html)
Nice things about using keep for this:
- access from any device
- nice UI
- supports images
- reminders to review a note
- half decent text editor
- searchable
- categories
- free
cons:
- mixed in with other notes in the default view
- hard to export for review in other formats
- have to manually set the interval (e.g. using reminder tool to set 3 days from now, then 1 week, then 1 month ect). This is tedious
- not suited for larger documents
- not really suited for flashcard style of studying
Other things I've tried:
- folders with text files
- ankiweb