Links

Below are links, grouped into categories, to sites that I find useful and/or interesting.

arXiv - a repository of electronic preprints (known as e-prints) approved for publication after moderation;
Google Scholar - a search engine for scholarly literature;
AustMS/ARC Journal Rankings;
MSC - 2010 Mathematics Subject Classification Code Database;
OEIS - the online enclyclopedia of integer sequences;
ORCID - provides persistent digital identifiers to distinguish researchers from each other;
GAP - a system for computational discrete algebra;
GAP semigroups package - a GAP package containing methods for semigroups, monoids, and inverse semigroups, principally of transformations, partial permutations, bipartitions, subsemigroups of regular Rees $0$-matrix semigroups, free inverse semigroups, and free bands;
Math Overflow - question based (research level);
Mathematics Stack Exchange - question based (general);
Reddit's Math Subreddit (the quality of Reddit has degraded hugely over the years, not just from eternal September);
Math Bin - a paste tool for LaTeX/mathematics;
The Grammar According to West - some useful observations and suggestions for writing mathematics;
Advice to a Young Mathematician - Chapter VIII from The Princeton Companion to Mathematics.

cplusplus.com - descriptions for the most important classes, functions and objects of the Standard Language Library, with descriptive fully-functional short programs as examples;
Project Euler - problem based;
Sublime Text - my favourite text editor for programming;
GitHub - free hosting of git repositories and static websites;
GitLab - free hosting of git repositories and static websites;
Stack Overflow - question based;
Reddit's Programming Subreddit;
Reddit's C++ Subreddit (this subreddit has been taken over pretty badly);
Paste Bin - a paste tool for text and code;
Code Pad - an online compiler/interpreter, and a simple collaboration tool;
Google's guide to becoming a competent software engineer;

Ubuntu - Debian-based Linux operating system;
Official Ubuntu Documentation - created and maintained by the Ubuntu Documentation Project;
Ubuntu Community Help Wiki - user-created and maintained wiki referencing various Ubuntu-related guides, tips, tricks and hacks;
Official Ubuntu documentation for installing Ubuntu on a macbook pro;
Arch - simple, lightweight linux distribution that preferences developer experience over user experience;
Arch wiki - well-maintained source for Arch Linux documentation;
Reddit's Linux Subreddit - question/discussion based (also pretty bad these days);
The Art of Command Line - a reasonably comprehensive bash guide.