First developed by Christopher Seed, the piano is a mirror image of a standard piano.
Seed, himself a left-hander, built a piano with the keyboard in reverse, so that the bass register notes were at the top of the keyboard and the higher pitched treble notes were at the far left. He believes that doing so allows a left-handed player to capitalise on his or her strength, expressiveness and agility from that hand.
As most piano music is written with the melody in the right hand supported with chords in the left (as in most cases - the melody is usually carried by higher pitched notes than the accompaniment), reversing the keys makes more sense for a left-handed player.
According to www.lefthandedpiano.com "the instrument was first built by Poletti and Tuinman Fortepiano Makers of Holland, one of the finest firms in the world. It is a mirror-image piano based on an instrument built by Conrad Graf in Vienna around 1826. The left-handed piano was completed in the summer of 1998 and exhibited at the Bruges International Music Festival from 27 July to 1 August 1998".
The piano is more than just an interesting experiment - it is in production currently by German piano maker Blüthner.
See a performance on the left-handed piano in the below video.