A free program for Android, by Nostalgia Emulators.

Nostalgia.GBC is the best GBC emulator for Android. It’s a high-quality emulator with a modern and elegant design. Here, you can fully customize the virtual controller and adjust the size and position of the buttons. It has turbo buttons and an A+B button that is perfect for gaming. In addition, there are 8 manual slots where you can save your game progress, and you can share them via mail, Skype, etc.  

Nostalgia.GBC comes with a simple, clean, and user-friendly interface, which makes this emulator much easier to use and navigate. The best thing about this is that you can download it on your device completely free.