Mathematics

Hovhannes Khudaverdian
Nick Higham
James Montaldi
Yuri Bazlov

Gnuplot

Gnuplotting
Not so frequently asked questions

Vim

Notmuch-Vim

Manual

cht.sh

Perl

Learning Perl
Intermediate Perl
Mastering Perl
Perl Power Tools

Community

StackOverflow
tilde.club
Drop

Mac

MacPorts

Linux

ArchLinux