The Power UI is a downloadable user interface for The Lacuna Expanse that is intended for power players. It does not have all the features of the official clients (yet), but it does make managing the task of a large empire easier.
You can download it here.
You'll need to install Adobe Air to use this client.
The current version is 0.5.6 released on 04/29/2011.
Also check out the clients and utilities page.