It's just a very simple batch code that I wrote. It changes your Minecraft playername.
It's really usefull if you wanna play with your friends on your server, but they don't have a real minecraft account, so all of them will have the name "Player" which will result to everyone except for one, to be kicked.
It's just a batch file, right click - edit, to view source.
Or you can go here for pastebin.
Note that this, only works on servers that have online mode on false: online-mode=false
And singleplayer ofcourse.
Here's a screenshoot...
Oh and if you get outdated client or whatever. Simply go to /%appdata%/.minecraft/bin/ and delete any old versions.