The interface is clunky and extremely ugly; I first used this software 10 years ago on Windows and it looks much the same now as it did then, give or take a few new button icons. However, it's a mostly well-written piece of software that is really good for what it aims to be: a points and polys modeller. There are some real oddities to it — no search in the Help menu as per every other application under 10.5, and Boolean operations that seem just not to work a lot of the time — but you won't notice most of the time.

My tip: go to /Applications/ac3dmac/tcl, open ac3d.tcl in TextEdit, search for the text "proc bypass_system_dialogs" then add a hash character to the start of every line, down to the one with a '}' just after the text "puts "system file dialogs bypassed"" (some of them already have hashes, add or don't add at your discretion). Following that, the editor will run with proper native file selectors for save/load, less ugly pop-up boxes and the normal OS X colour wheel. It seems there was some bug way back in 10.4.8 that precludes this being the default program configuration.