Fast real-time backup? Haven't tested but it sure looks interesting -- beta versions are free and beta testers are eligible for free licenses. The site feature summary:
Real-time, periodic or manual backups; Delta file copying; Precise file replication; Intelligent error handling; Small is beautiful; Powerful and intuitive file filtering; Streamlined and uncluttered user interface; NAS and HDD friendly; Software updates; Light on requirements
Is it portable?
> bvckup.exe -c path-to-bvckup-configuration-directory
If the "-c" is omitted, then the program defaults to using %LocalAppData%/Bvckup folder.