PYBAG implements a portable bag and is intended for fast synchronization and backup. It lets you use a portable digital storage device to carry your electronic documents similar to the way you can use a bag to carry paper documents. You can synchronize the bag with your original files easily. If a synchronization conflict occurs, it will be reported. You can specify rules for automatic conflict resolution. With PYBAG, you can backup files and synchronize any changes made to the original files with the bag. The synchronization process will only copy changed files. The program is cross-platform and independent from the OS and filesystem. You may easily synchronize files between Windows and Linux, for example. Symbolic links are supported on all systems (if the OS or filesystem does not support symlinks, then they are emulated). This program has a GUI and a command line interface.