- kernel? uname -a (thanks, DaWuzzz)
- How long has the machine been running? uptime
- Who is logged in? finger
- Short general information (hardware, kernel): sysinfo (package hxtools)
- Which distro am I on (for remote administrators or extremely confused users)?
(more information here)
- Did I install this package? rpm -qa | grep -i <any part of package name> (you need grep if you don't know the exact package name: rpm -q doesn't like wildcards)