For the moment, it is only available as a Chrome extension. But thanks for your feedback, we'll definitely take it into account.
Additionally, if you happen to be a Business Class Trello user, we just released the Elegantt Power Up (http://elegantt.com/trello/powerup/) which is compatible with all modern browsers. The Power Up is not as feature rich as the Chrome extension but it will give you a good overview of your board progress out of the box.
Unfortunately Elegantt for Trello is not currently available as a desktop app, but I'll forward your feedback to the team.
I'll definitely get back to you if we need beta testers for a Google Apps integration. Have you checked out the Chrome Extension for Trello? I'd love to get your feedback on it.