This is my attempt at a QtCurve theme based on Apple's Platinum style from System 8 and 9. QtCurve is a bit limited, but it's a decent theme. The only really bad issues that I encountered were that I couldn't shape the tabs right, and I couldn't have a separate highlight color for menus and views. In response to the latter I created two colorschemes with different selection background colors. You can choose which one you like better.
The one pro of using QtCurve (apart from the fact that it's fairly flexible and requires no specialized knowledge) is that it is very easy to make it color scheme agnostic, so if you've ever thought to yourself "You know, I like the widget style of OS9, but I'd really prefer CDE colors," Then you're in luck! Just download that one CDE colorscheme and use it with this widget style. On the other hand you're on your own for finding a GTK3 theme that looks even remotely similar (Though you could at least do colors with Oomox)
In hopes of encouraging collaboration (even though I think I might be the only person still using QtCurve), I'm going to try to make a git. Eventually I hope to make a KWin theme to go along with this, but I basically am hopeless at making my own pixmaps/svgs at this point, so I'm not sure if I'll ever finish this.
At any rate, I hope somebody other than me appreciates this.