Note: The Kingdom of Windermere features elements from my previous AU projects such as both Philippines AU's and the Republic of Corpus Christi AU. Unlike those other AU's, Windermere is set in a completely alternate world, similar to the Strangereal setting of the Ace Combat video games. This post ...
I use KolourPaint, which has a similar interface to MS Paint but with additional features such as transparency support and more undo/redo levels. However, it is only available for GNU/Linux systems.