I previously used Vitamin-R 3 for a few years. It has a feature very similar to Session's "presence" feature, i.e. it plays a sound every few minutes to remind you that you are currently in a session.

However, Session's implementation doesn't work very well for me because of the sound: I keep thinking that there's been an error somewhere and it's a super short sound. Vitamin-R has a dropdown menu to choose a sound from (see screenshot). I really like their "clock ticking (4s)" sound, as it gives me this "Pomodoro" vibe.

While I am particularly interested in changing the sound for the "presence" feature, maybe users would be interested in being able to change the notification sounds, either from a selection or possibly even being able to add custom sounds? I assume this is somewhat tricky due to cross-platform sync of settings?