An incredibly helpful feature from our legacy iOS platform is voice messaging. Our advanced backend allows you to send voice snippets to other users, play back other people's messages in slow-mo, use automatic transcription, and learn words right from what other people are speaking.
I personally have found this to be instrumental to improving my listening skills, but want to throw this idea in the hat to see if people would like to see this feature brought to web. We have it about half implemented and are wondering if we should finish it!