SDL 2.0 is freely available under the terms of the zlib license, and SDL 1.2 is freely available under the GNU LGPL license.
Both may be used in both free and commercial applications.
You can read the detailed license text at libsdl.org's license page.
Yes!
SDL 2.0 can be freely embedded either as static library or as linked .dll (or .so or other sorts of dynamic libraries).
For SDL 1.2, the GNU LGPL license requires you to adhere to this additional restriction:
If you link dynamically (via .dll's, .so's or using other dynamic linking devices) then you do not need to do anything.
If you link statically (include the SDL source inside your project when you compile) you have to provide some way for your customer to relink your application with a custom version of SDL.
The details are available at: libsdl.org's license page.
Yes! However, for SDL 1.2 you will either need to publish the source code of your program if you're statically linking, or provide tools and object files required to link against another version of SDL.
The details are available at: libsdl.org's license page.
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.
Each of the demos has its own licensing restrictions. See the "COPYING" file in each demo's source directory for more information on a particular demo.
Unless otherwise noted, all wiki content is licensed under Creative Commons Attribution 4.0 International (CC BY 4.0).