What are good SnapCAD Alternatives that run on Mac?

I don’t think there’s much at all. The closest is Bricksmith, which is also based on LDraw just like SnapCad. But the interface is not all that good.

I would recommend OnShape for Cloudbased there’s a recent VexIQ parts library by @jrp62 (https://www.vexforum.com/t/help-with-vexiq-parts-library-for-onshape). OnShape is browser based and our team has used it on Macs, PCs, and Chromebooks. I assume it works on iPads as well since we used it with Safari on Macs. OnShape is free for educational use.

If your students find OnShape a of a learning curve, and like the snapping feature of SnapCad and something a bit easier, I would recommend LDCad.