A very nice sectioned list of unix command - http://en.wikipedia.org/wiki/List_of_Unix_programs

Backup a list of directories - http://linuxintegrators.com/acoliver/code/?permalink=x-0272.html

A quick reference - http://www.cs.usfca.edu/~parrt/course/601/lectures/unix.util.html

Tuning cheat sheet - http://www.performancewiki.com/linux-tuning.html

Common and difference between systems - http://www.thegeekstuff.com/2012/01/linux-unix-kernel/

BSD for linux user - http://www.over-yonder.net/~fullermd/rants/bsd4linux/01

Actually a quick tutorial - https://sanctum.geek.nz/arabesque/series/unix-as-ide/