I know that both `apt-get` and `aptitude` are command line package management interfaces on Debian derived Linux, with different options, but I'm still somewhat confused. Under the hood, aren't they using the same APT system? 

Why does Debian maintain these parallel tools? (Bonus question: what on earth is [wajig](http://manpages.ubuntu.com/manpages/maverick/man1/wajig.1.html)?)