TeX related:
Overleaf for latex on the web - no installations!
LyX for what-you-see-is-what-you-get editing
IPE for what-you-see-is-what-you-get editing of slides and posters, and also drawings with tex annotations. Download my stylesheets here.
MyScript for the latex code of entire equations when you handwrite
MathPix for the latex code of screenshots of equations
QuickLaTeX for typing some LaTeX and getting a graphic out
Texcount for counting words in tex documents
Instructions for making a bibitem for arXiV, (change these settings first).
Diagram of all the lengths used in lists.
Typeit for copying unicode math symbols into emails

Other Tools:
Sejda for PDF editing, e.g. combining and deleting pages
Printing PDFs 2 pages to 1 page (settings for LinAl book: 0mm outer margin, 15mm inner margin)
Pixlr for editing pictures
iPiccy for making photo collages
Color-Hex for finding RGB, HSL etc of colours
DiffChecker for seeing the differences between two files (or the listings between two directories, if used with these instructions.)

Online Teaching Tools:
PDF Annotator ($500HKD or 30-day free trial) for electronic-writing on slides
Avidemux for trimming videos within seconds
Ipevo Visualiser for showing writing on physical paper over zoom

Mathematical Mathematics Memes
PhD Comics (slow updates)
Spiked Math (slow updates)
Research in Progress tumblr (slow updates)
TruthFacts (slow updates)
What do grad students in math do all day, featuring vacuum cleaners
The snake-fight portion of your thesis defense

Superior stationery:
Erasable gel pens, great for doing research in more than one colour. If you know where to find coloured refills in HK, please let me know!

Permutation toys:
Skewb (currently in McGill)
Mosaic Cube (currently in McGill)
Square One (currently in LaCIM)
Curvy Copter (currently at HKBU)
Megaminx (currently at HKBU)
They are for decoration / destress purposes only, I don't think about solving them. The first three are from the Now Store in Causeway Bay, Hong Kong, which has since closed. The fourth is from their online store. The fifth is from a toy shop in Kowloon City. If you know any other physical stores that sells them, in any city, please let me know!

amypang [at] hkbu [dot] edu [dot] hk