Not sure where you found a subscription to Anki, but it's free and open source: https://github.com/ankitects/anki
The iOS app is a one-time payment though.
This article is definitely not written with an unfamiliar reader in mind though, that's for sure.
Anki is an open source app: https://github.com/ankitects/anki
Only the iOS version costs money, which is probably their only revenue stream.
Not sure, but Anki is open source, so you might have some luck there.
Anki flash cards (floss) do use spaced time learning algorithms that are also easily adjustable to personal preference. Anki has native mobile/desktop, cli and web clients. The big community also provides shared decks and vast plugin ecosystem like auto text-to-speech and imagery.
I haven't seen any of these tools doing anything that anki doesn't — why not contribute to it instead?