Gunkimono is a retheme of Heartland, with just a few rules tweaks (like having a selection of tiles to add to your hand, and no double tiles with the same color on both sides).

Skyways had Heartland as a starting point, but went in a much different direction and I hope it will also get published some day. But I know a lot of fans were more interested in a Heartland reprint with a more fitting and exciting theme for its cut-throat gameplay.