I think anki is still probably the way to go. It doesn't store your cards in plain text, they're in a sqlite database instead. I use ankipandas[0] to read, manipulate and analyze my cards though.
Anki checks two of these boxes, but the data is stored in SQLite. It is a nice program, open source and actively developed, with many online resources available and a large community.
My advice would be, if you happen to already write your notes in some plain text format, to create your flashcards in your notes. E.g. if you use one of the fancy new PKM tools like Logseq/Obsidian/etc. you can use one of the available plugins to sync to Anki (or roll your own script, thats what I do).
For me thats a solution with which I feel very comfortable (and I am rather picky and have tried out a lot of tools and workflows). Main advantages for me:
1. your notes and SRS questions are not separated
2. you have full control over your data
3. you don't have to use the editor of any SRS app, instead you can use whatever tool/editor you are most comfortable with
4. By syncing to Anki, I get all the nice stuff that comes with Anki: mobile clients+sync, nice statistics, endless styling customizability.
- Sync across devices
- Plain text representation of cards
- Nice mobile interface (I anticipate usually using my phone, but don't want to author cards on the phone exclusively, or be locked into an app)
Is the answer anki+ankiweb+ankdroid? Is there a better alternative?