Hi all!
Now CAST II Engine - the only free engine with megatexture support.

Full SDK - 19.4МБ.
Landscape demo only - 7.7МБ.
Other downloads

There is no texture by default. It's compiles from mega.bmp file on first run (takes time). You can take any image, convert it into .bmp and place in the demo's folder. To replace picture replace mega.bmp and delete mega.dat.
If random.bmp exists it will be randomly placed over megatexture every time you run the demo (and stay here after close).
If you have no picture for megatexture you can use the landbig.jp2 file coming with the demo. It should be converted from jpeg2000 to .bmp.

Megatexture can be editied in CASTEd in real time. Also there is experimental post-fx pipeline. You can turn on bloom effect by double clicking on camera object named "BloomCamera" (need to load land.cbf first). It's only proof of concept yet.

At Official site a community forums opened. You are welcome to participate.

If someone wants to help with OpenGL and/or Linux support - please contact me.