ClanLib is a cross platform C++ game SDK, currently supporting Microsoft Windows, Linux.
It has a BSD style licence, meaning that you can also use it (or parts of it) for commercial products.
The following display targets are supported:
GL (OpenGL V2.0 and above)
GL1 (OpenGL V1.3)
GDI (Software rendering using SSE2 instructions)
SDL (Using SDL library)
Example screenshots can be found at: http://clanlib.org/examples.html