Q: What license is Mike's Sprite Editor under? A: Mike's Sprite Editor is licensed under the GPL v3. This means you are free to use, distribute, and modify the program to fit your needs. Images produced by Mike's Spite Editor are yours, and are there are no restrictions on how they can be used.
Q: Will Mike's Sprite Editor be ported to other Operating Systems? A: Currently, there are no plans to do so. This program replies on the Win32 API for most of its functionality, and changing this would require almost a complete rewrite. As it stands, it should be able to function properly under Linux using WINE.
Q: Why isn't there an Eraser (or similar) tool? A: To be honest, including one seem redundant. All this tool would be is a clone of the existing Pencil tool that draws using the background color when you use the left mouse button and the foreground color when you use the right mouse button. Just draw with the right mouse button; you really don't need to change to a different tool for this.
Q: Will this support working with layers? A: Originally, the answer was no. However, it's become obvious that such a feature will be needed. Thus it's only a matter of time before a solution is worked out.
Q: Will Mike's Sprite Editor be available in languages other than English? A: Eventually. Right now, the primary goal is getting it (mostly) bug free and mostly feature complete. Once that's done, focus can shift into translating things. I'm specifically hoping to get this translated into Spanish and French, at the very least.