Recovery Tools Index
Ventoy
Ventoy
Allows you to use a single, large USB drive to store and boot from multiple bootable ISOs. Super helpful if you're distro hopping or want multiple rescue CDs. Sometimes I've had mixed results if SecureBoot is enabled, so your mileage may vary.
Hiren's BootCD
Download | Hiren's BootCD PE
Basically a stripped down Windows recovery OS with a ton of tools for repairing and recovering systems
SystemRescue (formerly SystemRescueCD)
SystemRescue - System Rescue Homepage
Linux system rescue toolkit available as a bootable medium for administrating or repairing your system and data after a crash.
DBAN (Darik's Boot and Nuke)
Data Removal: Darik's Boot and Nuke - DBAN
Does what it says on the tin; systematically erase hard drives.