Since releasing back in 1997, there has never been an RTS quite like this one, and it baffles me there's never been a remake or sequel in all that time.
Very much a product of its time, The Tone Rebellion features a quasi-3D style that will bring to mind contemporaries like Alien Legacy or Septerra Core.
As a leader of the jellyfish-style Floaters, your goal is to free your people from the tentacles of the mighty Leviathan. With light RPG elements and a totally different faction selection than your typical RTS, this is a game that deserved more attention than it ever got.
Sadly, this is one of those classic games that never made it to digital outlets. Your only options now are to find a disc floating around somewhere or hit up an abandonware site. Make sure to give it a vote on the GOG community wishlist page if you want to see it make a proper digital return!