https://github.com/pshtif/Genome2D/downloads ist the only Stage3D 2D engine with FlashPlayer 10 compatible (no wmode setting) fallback to software Rendering i am aware of.
Unfortunatly they dropped this great feature after 0.35 Version. But i need a Stage3D 2D engine that has such fallback. Any other Engine out there with support for that and active development?
EDIT: Background: I need hardware rendering only on mobile were i can assure a correct set rendering mode. But in the web a lot of game portals do not support any wmode setting. But my game will run fine on a desktop in softwaremode.
This fork of Away3D Lite does exactly what you want (complete description here). It is a 3D engine though. You can overcome that “problem” and make it a 2D engine using a fixed camera and an orthogonal projection.