I started a Linux port of the engine some time ago, and got pretty far, but then I kind of lost interest and felt it was better to continue making the actual game instead, so I put it on hold. It's definitely something I want to do at some point in the future, especially so I can get things more easily running on Mac.
Viewing post in Death Strike comments
Thanks for the response. It is good to know that you're already planning a port for Linux-based OS. The game's page says it was made with Aseprite and that already has an Ubuntu version so porting should hopefully be a bit easier.
I'm hoping this game is successful enough that you can make future games and do so on a more easily cross-compatible engine like Unity/etc.
Well Aseprite is only for the graphics when I do my pixel art, the actual engine itself is made by me, and it depends on very little. The reason for going with my own engine is that it's a lot of fun to make things yourself, and I want to program in C++ so Unity and the likes have never really interested me. My current engine is somewhat similar to Unity, but made for 2D pixel perfect graphics and allows you to do all your work in C++, even scripts, which is awesome.