120years.net is the ongoing web project of Simon Crab. Started in 1996 the project outlines and analyses the history and development of electronic musical instruments from around 1880 onwards, so although the title is now almost 20 years out of date it has become something of a brand name.
The project defines 'Electronic Musical Instrument' as an instruments that generate sounds from a purely electronic source rather than electro-mechanically or electro-acoustically. It is not designed as an exhaustive list of recent commercial synthesisers or software packages as the project focusses on electronic instrument design and development previous to 1970.
The earliest "electronic instrument" that the Crab discusses is the "Golden Dionysis", an early one-off keyboard instrument built by the Czech theologian and pioneer of electrical research Václav Prokop Diviš (1698 – 1765). However when reading through this entry into the list, you soon learn that the "Golden Dionysis" is more likely a practical joke designed to electrocute the performer at will by the inventor....
This is just one of the many interesting stories that litter the history of electronic instruments. If you are at all interested in this history, then I would suggest that you take a look at this excellent resource.
More info at 120years.net