I couldn't find a reliable cubemap slicer, so I made one.
This is a super simple website built using Webpack. Upload a cubemap image to the site and it will download a ZIP of the split pngs, seperated into top, middle 1, 2, 3, and 4, and bottom.
Live version available via Repl at https://cubemap.mikeylab.com
Contributors: Aidan Raney, https://devaidan.com/