I spoke to the developer personally after a comment was posted on their Kickstarter a few days ago, noting that they were unsure if the Linux and Mac versions were going to happen. Since this was buried in a comment on a Kickstarter post, I wanted to find out what was going on. The developer explained the situation, so I advised them to be open and honest and make a proper announcement on it.
Now they have done so, in a larger post on Kickstarter and it's not a great situation. It's a case of a small two-person team biting off much more than they can chew. It goes over a bunch of issues they faced, along with funds getting low and a publisher leaving them "due to the delays", along with "personal and health issues" and so on. One of the developers is going to be moving onto other things too, so there will only be one person left to deal with everything.
The good news, is that they said refunds will be offered "as we get any revenue from the releases". So if you did back it on the Kickstarter back in 2015 it might be time to seek that refund.
Always a shame when things like this happen. Game development is a long and expensive thing to do, without seriously good planning so many things can easily go wrong.
It has been added to our dedicated Crowdfunding Page.