The latest version of this library is available from GitHub: https://github.com/libsdl-org/SDL_ttf/releases
This library is a wrapper around the FreeType and Harfbuzz libraries, allowing you to use TrueType fonts to render text in SDL applications.
See the header file SDL_ttf.h and the example showfont.c for documentation on this library. This documentation is also available online at https://wiki.libsdl.org/SDL_ttf
Be careful when including fonts with your application, as many of them are copyrighted. The Microsoft fonts, for example, are not freely redistributable and even the free "web" fonts they provide are only redistributable in their special executable installer form (May 1998). There are plenty of freeware and shareware fonts available on the Internet though, and may suit your purposes.
You may check the API reference by category.
This library is under the zlib license, see the file "LICENSE.txt" for details.