VirtualPiano

VirtualPiano is a reliable application that creates a virtual instrument on your desktop, allowing you to play it via keyboard or mouse.
With a self-explanatory name, VirtualPiano comes with predefined keyboard shortcuts to better control the application, but also with a rather simple interface that makes the whole task a breeze.
Although it's a good thing that it supports shortcuts, VirtualPiano doesn't allow the user to change them, so you're stuck with the standard settings. Each keyboard button is assigned to a piano key, with some special settings regarding the pedal effect.
As you can see, VirtualPiano provides just a limited level of customization, so it only allows you to save, load or edit a voice, choose between piano keys and accordion left hand keys, define the pressed key color and access the MIDI device settings for further configuration.
Plus, it provides dedicated tools to control octaves and semitones, with predefined shortcuts to adjust them on the go while playing the virtual piano.
All in all, VirtualPiano is nothing different as compared to the other virtual pianos on the market and while it provides a very user-friendly GUI, it lacks a configuration menu as well as a help file that could provide assistance to beginners.
Nevertheless, it's still one of the apps that if used together with an external device such as a video projector can turn out to be great for teaching purposes. Professional musicians, as well as amateurs can enjoy it alike.