Personally, I've used Anki to keep remembering/revisiting the concepts that I use for a while and then move onto something else. Common APIs of programming languages and their standard libraries is one such area. I've found that while it's not really difficult to learn and get into the flow of using a programming language (or history, mathematics, physics for that matter), it's more difficult to try using the same knowledge after a break of few months.
My main language at work is C# and Web Development, but I keep trying to learn other languages and domains in my free time. If I do not use the knowledge for a few months, I forget everything. But with Anki I have to just open the app for around 10 minutes a day and it helps me to recall such concepts in a timely fashion.
I would suggest everyone who has the time and faces similar issues should give it a shot.