VST2413
VST2413 is an attempt on deriving a chiptune synthesizer based on the PC emulator technology. This VST plugin emulates the Yamaha YM2413 FM synthesizer chip (as known as OPLL), and can resemble the sound of old game consoles and PCs, such as SEGA Master System and MSX-AUDIO.
The original source code of the emulator (emu2413.c) was written by Mitsutaka Okazaki, and due to its great design and quality, it can replicate the exact sound of the original chip at extremely low CPU load.
The plugin and its source code are available under the open source license.