The FreeType engine has been developed to provide TrueType support to a great variety of platforms and environments.
Note that FreeType is a library. It is not a font server for your favorite platform, even though it was designed to be used on many of them.
Notice too that it is not a complete text rendering library. Its purpose is simply to open and manage font files, as well as to load, hint and render individual glyphs efficiently.
You can also see it as a "TrueType driver" for a higher-level library, though rendering text with it is easy, as demonstrated by the test programs.