Kindle Sync is a freeware and portable software which makes it easier to transfer books from your computer to Amazon Kindle. The program can only copy and sync .Prc files, which are Mobipocket files from your PC to Kindle.
It maintains the same directory structure on the Kindle. You can also convert your documents and other PDF files to .prc format by using the Mobipocket creator publisher edition and then use KindleSync to upload files to your Amazon Kindle.
KindleSync works on Windows 7 and other Windows operating system.