OperaGame

OperaGame is a user javascript for Opera browser, much similar to the frequently used Foxgame (technically it works more like greasemonkey). It has almost all features as Foxgame, and brings some new stuff also.

OperaGame can calculate server lag so it's much easier to phalanx someone. When your fleet gets phalanxed, it is possible to escape within 4 seconds - you can set your target planet and fleet, and then just press "next" and you're safe.
However, there is one downside - this script is not allowed. I'm not sure why it's illegal, but my bet would be because of the phalanx escape thing I just described.

There's a number of other useful features, such as highlighting debris fields, coloring alliance players or enemy players in galaxy view, showing finishing time for buildings or research, coloring circular or private messages and more.

Whether or not you can be caught with this is beyond my knowledge. I've seen people on banlist before for using OperaGame, but how exactly they got caught I don't know. If you move your fleet within 6 seconds, it is likely you will get banned if reported by your attacker. Other than that, I don't know if GO's can track what browser plugins you use. I do know, thanks to a certain visitor, that Firefox extensions can be tracked. It might help if you set Opera to identify as Firefox or Internet Explorer to websites: Tools > Quick preferences > Edit site preferences > Network > Browser identification.
I'd recommend using this on your multiaccount only.

You can download OperaGame from the official forum (there's an english section if you need help), and while you're there check out some other cool related stuff such as translations to other languages.
If you need help with installing the script, or you want to learn more about Opera's user javascript, visit Opera Wiki.