Apache:
Apache 1.3 Quick Reference Card
https://refcards.com/refcard/apache-forda
Checkpoint FW-1/VPN-1:
German: Die 100 wichtigsten Check Point VPN-1-Kommandos
https://www.galileocomputing.de/download/artikel/346/galileocomputing_poster_check_point_a3.pdf
Cisco:
Ciscopedia: A new Windows-Help-formatted File with a big Reference for Cisco command
https://www.google.de/search?q=ciscopedia-v3
Perl:
Perl Regular Expressions
https://refcards.com/docs/trusketti/perl-regexp/perl-regexp-refcard-a4.pdf
And some more see: