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Debian specific tools/apps

Hello I’m new to Debian and wanted to know what are some good Debian specific tools/apps I should know so I don’t write emails like this.

I know of
1. Dpkg
2. Apt-file
3. Apt
4. Aptitude 
5. I know how to use backports for stable

Is there anything else I should know that can help me find answers quick and help me maintain my system