To remove the 'localhost:nnnn' or 'ElyBy' in the minecraft main menu and F3, add -Dauthlibinjector.noShowServerName to the java arguments in UltimMC settings. In case if you are using MacOS/Linux then additional step is to make a script UltimMC executable by using the command chmod +x UltimMC in the terminal As your email use your username, and then type a random password or use ElyBy account.Go to account settings, and you will be requested to use email and password.Download pre-built binaries for your system.

Do not use the inbuilt option, as that downloads the MultiMC launcher instead (this will be fixed in a future version). To update the launcher replace all replaceable files and folders with the newer one from the above link. Please don't bomb MultiMC developers if something gets wrong using this launcher. This software is not related to MultiMC developers and provided without any warranty.

This is a 'cracked' version of a popular Minecraft launcher that lets you play the game without a Mojang account.

Minecraft launcher cracked linux