As of SDL 2.0, the software is freely available under the terms of the zlib license.
You can read the detailed license text at http://www.libsdl.org/license.php
Yes!
SDL can be freely used in commercial applications either as a static library or as a shared library (recommended!)
Yes!
There are no restrictions on using SDL in an embedded environment.
No!
You may use SDL completely free of charge.
Yes, code from the test directory and from the examples in the documentation is placed in the public domain. Anyone can use it for any purpose.
The wiki content is under the Creative Commons Attribution 4.0 International license.