

2 that stand out to me:
When I successfully got virtualbox to boot my windows xp partition inside Linux because I needed to run some software for school.
When I figured out how to use qemu-nbd to mount a qcow2 image backed by a physical block device in order to run non-destructive filesystem repair and file recovery with test disk. Did that for a while for my university IT help desk to quickly save files off failing disks.
Would you believe me if I told you this is how conda works? :P