4Front E-Piano is a small single sound instrument without any settings that reproduces a timbre, which is similar to DX-7 type e-piano. It is available as VSTi for Windows, and as an AudioUnit, VSTi and RTAS for Mac (see enclosed readme file).
This instrument is small on memory and CPU usage and was found useful by many users and software developers as a plug&play e-piano module, which does not require any configuration or adjustment.
Though this goes without saying for professional users, I still had a frequent question on how to use this plugin from people, who are not familiar with this technolog. One should note, that to make use of this software a plugin hosting software is necessary, such as Topten Cantabile software. A MIDI keyboard is also preferred, as it is something almost essential to create a computer music these days.
There is also 4Front R-Piano, which replicates a different type of E-Piano.