One of the better Gameboy Color emulators for Windows Phone has made a hasty disappearance from the Windows Phone Store.
VGBC8 by M.K. has been unpublished from the store, and while the reasons are not known, emulators have long skirted the line between legal and illegal, making it no surprise the app has been pulled. There are plenty of other emulators in the store however, so it does not appear to be a general purge.
When Windows Phone 7 launched there was initially a ban against emulators, but this was rapidly relaxed, and with Windows Phone 8 allowing native code, which allows easier porting and improved performance, this has been one of the growth areas recently.
If you do have the app installed it should continue to work, but of course you will not be able to re-install it once it is uninstalled.