Freemarker can support multithreading
In a multithreaded environment Configuration instances, Template instances and data-models should be handled as immutable (read-only) objects.
But can it use parallel execution as pebblet when rendering?
provide an ExecutorService to the PebbleEngine and make use of the parallel tag, you can have multiple threads render different sections of your template at one time. This is especially useful if one section of your template is costly and will otherwise block the rendering of the rest of the template.
I also found an old Freemarker extensions which I wonder if it can allow it:
This library provides two ways to render asynchronous models: futures and callables. Futures are asynchronous computation results and callables are tasks that should be computed asynchronously. Callables require configuration of an executor service