The source code is released under the ISC license, which is functionally identical to the BSD license. As such, it can be freely modified and reused in any project, either proprietary or free. It is written in 100% ANSI standard C. Each data structure is written to be independent from the others in the library, allowing particular data structures to be included in projects as needed.
The library includes an extensive test suite. You can read some information about the testing strategy used for the library here. If you do find any bugs, please report them on Github.
The latest release, v1.2.0, can be found here. The documentation for the current release is also available.
The current source code can be found in the Git repository.