GT-Engine is a new implementation of the default groovy template engine in Play Framework 1. GT-Engine is faster and uses less memory.
You can now use GT-Engine in Play 1 using the module faster-groovy-templates which is a drop-in-plugin replacing the default template implementation.
UPDATE: The module is now available in the Play Framework module repository
There also exists a Play 2 module that makes it more easy for you to port your Play 1 application to Play 2.0.