zBoy
a multiplatform, full-featured GameBoy classic emulator
zBoy is a multiplatform GameBoy emulator that provides a load/save feature, can perform PCX screenshots either manually or automatically (every few seconds) and emulates an internal battery for ROMs that were designed to use one (this allows to use the internal save option provided by such games, remember highest scores, etc).
zBoy supports some additionnal features, too, like intelligent saving of hi-scores for some games that aren't able to save their hi-scores table by themselves because of the lack of a battery-backed RAM on the cartridge, and improving screen's resolution output using graphic algorithms like Scale2x, Scale3x, eagle... Here you can see a comparison between graphic algorithms supported by zBoy. This is also one of the very few GameBoy emulators that provides a 2-gameboys link emulation, which makes it possible to play some games in 2-players mode on a LAN.
The emulator is available for Linux, DOS and Windows (but should compile for other systems, too).