Nothing appended to folder name is for Win 32
-x64 appended to folder name is for Win 64
-Linux is for linux and Mono versions less then 4 (arch doesn't matter) (mono -V will display version) (Depreciated/unsupported/not provided)
-Linux-Mono4 is for linux and Mono version 4 (arch doesn't matter) (mono -V will display version)
