GSi (Genuine Soundware and instruments) is an independent Italian software developer founded in 1999 by Guido Scognamiglio, who serves as the company's main programmer. The name derives from Scognamiglio's initials, and the company specializes in physical modeling sound synthesis with a particular focus on emulating classic electromechanical and electronic keyboard instruments.

GSi is best known for the VB3-II Tonewheel Organ Simulator, a virtual Hammond B3 emulation that has been refined over two decades of research and development and is widely regarded as one of the definitive software recreations of the instrument. The catalog also includes Organized Trio, the Farfisa-style Compact DeLuxe, the Red Animal transistor combo organ, and effects and tape echo emulations such as GS-201 MKII and TimeVerb-X. Products are available as VST, VST3, AU, and iOS apps.

Beyond software, GSi develops firmware and sound engines for hardware keyboards, and has collaborated closely with Italian keyboard manufacturer Crumar. GSi-branded hardware products, including the 5x5 and G.M. Lab modules, are manufactured and distributed by V.M. Connection in Italy.

GSi has 2 products cataloged on Equipboard, including Univibe & Rotary Effects Pedals and MIDI Keyboard Controllers.