Apparently "soon" there will be a somewhat playable game released for the "GG" engine.
FreeEmpires is using an engine known as "GG" (Gambas Genie), which is named after the "Genie" engine that AoE uses (and is also written in Gambas). Much of the FE and GG development is occuring side by side.
The
Gambas Genie page on the FreeEmpires website explains much of this and includes many "tech demos". I am not sure but I think you need to have the Gambas development tools to view them (may only be released as Gambas package files).
I happen too know that the most ambitious tech demo currently in production is an actual playable game. It is however, featuring "Genie's" as characters. Still an excellent demonstration of what FE could become. FE SR3 (Source Release 3) should include many of the features in that tech demo and possibly more. It is currently in development.
Unfortunately there are no dates for release of either the Tech Demo or SR3.