Complex sentence: In addition to the Vocaloid 4, the software itself also saw use in the Vocaloid Keyboard, which had first been announced in 2012, though prototypes of the Keyboard were finally unveiled in mid- 2015 though did not see commercial release.
Split into simpler sentences: In addition to the software side of Vocaloid4, the software also saw use via the Vocaloid Keyboard, which had first been announced in 2012. Prototypes of the Keyboard were finally unveiled in mid- 2015 and did not see a commercial release.