Here's a custom firmware for the AtGames Legends Flashback you might enjoy.
BurgerTime, Mappy, Street Fighter, Dig Dug, and their friends not enough for you? Here's the answer -- update your machine so it can load other files from the SD card, without losing the onboard games.
1. Back up your settings or save games first if you care about them.
2. Unzip this file and put it at the root of your SD card to perform the update. It will unpack to a 4.3MB disk image file named "arcade