[Typo3] Typo3 API and external applications

[LaPointe, Matthew]

Is there a mechanism whereby Typo3 is able to pass API information for
use in an external application?

Basically what I have is a typo3 site and a web application which can't
live inside typo3, and I want the external application to be able to use
the same template, including menu system. Is there a way to pass that
information to the external program?

Sorry if this is vague. I have been digging around for a few days on the
subject an am not having much luck. Not really sure quite what to look
for.

Matt