The KD-X is an unofficial spaceplane.
Based on warp technology, reaching its highest speed at half the thrust gauge, this thing is more of a weird engineer idea than a real tesbed or prototype.
Be aware that this bad boy can go up to 180 Gs, so if you have any kerbal pancakes to do, the KD-X is the thing you need !
KD refers to Kal-Drive, which it is based on, and not Kraken Drive.