Cassini is a guilty pleasure of mine. Cascade is another. It could be a stretch, but Dorcas also comes to mind. Here's a few more. Jocasta, Lucasta, Cashmere, Cassandrine, Cassarah.
I don't think Dorcas is a stretch - thank you for bringing that to my attention lmao. I love Cass names and I sort-of like Dorcas (enough to want to use it on a fictional character or at least in the sims) so having another option for the Cassy nn is good :)