MCSkin3D is a free, customizable, player skin editing and management studio.
It features simple tools to allow anyone to edit a skin file and upload it to Minecraft servers. It is completely free and open-source.
History
Started by Paril in late October 2011, MCSkin3D began as a small personal utility, but after a week of development, Paril decided to make it public. The project itself wasn't very well known at first, and was quite buggy. With time, the program got bigger and bigger. People started using it more and more, until one day, the MinecraftForums news writer published it on the homepage of Minecraft Forums.
In 2018, Paril announced that he has stopped developing MCSkin3D. Since then, Paril replaced it with the web-based successor PMCSkin3D.