Some things you can do with libguestfs ...
- differences between guests
- sysprep
- add users, change passwords
- security audits
- resize disk images
- creating templates & clone
- sparsify
- monitor
- dump filesystem contents (eg to tar)
- injecting files
- edit single files
- what's in a disk image?
- run stuff at next boot
- edit Windows registry
- edit Linux configuration
- multiple language bindings
- see: guestfs-recipes(1)