That's exactly what Aseprite (a pixel-art tool) does. I think it's great, I got it to build on Windows but eventually ended up buying it on Steam because it's so good.
Edit: Sources available, but not open source license as far as I understand the EULA. https://github.com/aseprite/aseprite
The license and FAQ are somewhat confusing as to if you need to pay for a license even if you compile from source.