Goomba is a Gameboy emulator for the Gameboy Advance. Beyond the advantage of being able to store many games on one cart, Goomba also includes save states and customizable borders. At least, my fork does. Also available are many palettes, along with the ability to make your own. This feature has lead to the creation of a small gallery, for your viewing pleasure.
The process to actually included custom borders can be quite complex, so I've created a tutorial which should help guide you through the process. Currently this project is somewhat ongoing. The most probable future release would include a cheat finder of some nature. But, it will probably be a while before any attempts to add this are made.
To actually add a custom palette requires a program called append. This name derived from the original design: creating a border file through the tool and appending it to the goomba.mba file. However, future changes have also made it possible to prepend to the .gb file itself in some cases, so the name is no longer very accurate. In any case, you have two main versions to choose from.
Kuwanger.net - Sort of like stag beetles in tubes.