A fork of SDL_widgets by W.Boeke, for reference purposes.
The master branch contains the code from SDL-widgets 1.0, with fixes and some non-breaking changes. See the 1.0 tag for a intact 1.0 version, or 1.0-fixes for a bugfix-only 1.0 version.
Please note that this version is compatible with SDL 1.2 only.
There is a SDL2-widgets version on the original author's website, compatible with SDL 2.0 - more info here.
Additionally, these github repositories also seem to host SDL2-widgets code:
(https://github.com/gale320/sdl2-widgets)
and not exactly, but related: