Tiles 2.0 and 2.1 have only the possibility to use JSP natively. Freemarker is usable through its ability to load JSP tags.
With Tiles 2.2 it will be possible to write templates with Velocity and Freemarker. In Subversion repository, two submodules have been created for this:
Documentation can be generated from the tiles-parent project.
Moreover, the support for future template languages is simplified by the presence of the tiles-template module, that expresses, in a template-language-neutral way, the tags to create Tiles templates.