Spacedeck, a web based, real time, collaborative whiteboard application with rich media support
It's used in the new Nextcloud Whiteboard included in Nextcloud 21 which is out today:
But I guess it'd be nice to be able to use without using Nextcloud too.
+1 for this. The fact that the docs warn strongly against installing Nextcloud apps makes Nextcloud's whiteboard app a no-go for me (unless that's not the case with this app in particular). My team and I are looking for something more robust (media support, etc.) than the currently-offered WBO app. We currently use Miro.