Boots directly from USB/CD, operating in RAM.

startx allows for mouse-driven troubleshooting. GParted: Re-partitions and fixes partition tables.

If you are planning to use this for a specific situation, let me know: Is it a or Linux machine?

SystemRescue is free, open-source software. You can download the official, secure ISO image directly from SourceForge or the official website . Detailed Story: The "Dead Server" Rescue