I'm not deep into geometry, but one of my favourite web apps / UI designs is the Polyhedra Viewer by Nat Alison [1][2], which shows relations, properties, and transformations in a very natural way.

Tom7's video on polyhedra properties [3] is also great, and taught me about the best Unicode characters (sic) [4]:

    ︘ U+FE18 Presentation Form For Vertical Right White Lenticular Brakcet

1. https://polyhedra.tessera.li/

2. https://aperiodical.com/2018/09/polyhedra-viewer-meet-nat-al...

3. https://www.youtube.com/watch?v=QH4MviUE0_s

4. https://www.compart.com/en/unicode/U+FE18