Is there any way to mark the flashcards as known or not known?

Hi,

I like the flashcard feature but am wondering if there is any way to mark the cards that you know well as "known" so they maybe appear less often and the ones that you don't know so well to appear more often?

No, that is not possible right now.  That would be a good feature to add.  Hopefully, the Rocket people reading this forum will add that to the multitude of improvements they plan for flashcards.  Hopefully, they will do that along with awarding points for working through the flashcards.  They do say they want to make it more like Quizlet which if they do will be a great improvement.

Yes, that would be great :-)

I think that having audio with the flash cards would also be an asset.

It would be an excellent learning feature.  Flashcard systems that more rapidly re-present cards marked as difficult (days to a week or so) and delay the repetition of cards that are easier (typically weeks to months) are known to greatly enhance the value of flashcard learning.  Really it is the key to all the best fact learning systems out there.  It is backed by decades of solid research in behavioural and cognitive psychology.
It would be a valuable addition to add it to Rocket.  Generally the idea is to select a number of cards to view each session and as each card is presented replace it in the stack at a point that corresponds to a date in the future when it should reappear based on the easy/hard score.  It's not a tough algorithm but it's impact of learning is marked.  It is one of the easiest ways to create the benefits of an 'effortful' learning cycle.  As a result can seem to be a bit of a struggle to remember the cards when they do come up but this is exactly why it is so very successful. It kills the illusion of fluency in learning that you get when you fly through material but don't actually take it in very well.  Spaced effortful repetition with flashcards produces significant improvements in long term recollection and should be built into the very heart of a great learning tool like Rocket.