What GTK+ 3 engines are available?

With the switch to GTK+ 3.x, most theme engines no longer work, and I personally only know of 3 (Adwaita, Unico, and Solidity).

What engines are available for use with GTK+ 3.x?

You have identified most of the engines ported (at the time of writing) to the full gtk3+ API.

In addition, there is 12.04 KDE support for oxygen-gtk3 (or for 11.10 via kubuntu-ppa-backports)

There is also a gtk3-engines-xfce package in Ubuntu 13.10.

Various references on google report that the development of the gtk3-engines package has ceased - not all the engines in the package were fully ported to GTK3+

For reference only: according to the notes of the gtk3-engines package in the ppa:gnome3-team/gnome3 - these were attempted to made available BUT don't expect these to work fully on oneiric.

• Clearlooks, the default GNOME theme, based on Bluecurve;
• Crux, formerly known as the Eazel engine;
• High contrast, which is used by some accessibility themes;
• Industrial, the famous engine from Novell (formerly Ximian);
• LighthouseBlue, another engine based on Bluecurve;
• Metal, which gives a metallic look;
• Mist, a flat and high performance engine;
• Redmond95, which provides a look similar to that of Windows;
• ThinIce.