• Resizable window
• Custom sizes
• A manual or an easy way to know how to manage files (open / save / export)

Thanks for your suggestion!

New suggestions:

• Compatibility with old versions
• A best way to report errors
• A maximun number of layers and width or height
• Best position and use of the help icon in the bottom-right
• Support different files extensios (like jpg, bmp, gif)

• An alternative to "middle mouse button" for laptops
• A light theme and/or a darkest theme