With Tropo WebAPI, you host your own code, so you can use any libraries available on your server, including those we created specifically to work with Tropo. These include our official libraries as well as ones contributed by members of the Tropo developer community.
With Tropo Scripting API, you can use most all of the "standard" libraries provided with that language's Java implementation as well as the Java API available in the JDK. We've restricted a few of them that may have security implications for our platform, but for the most part the full range of language libraries are available.
We will continue to evaluate the inclusion of additional custom libraries in each scripting languages, such as additional Python Eggs or Ruby Gems. Until then, the Java API is also available.