These are links to some online tools and resources that I find useful from time to time and recommend to whoever has not yet heard of them.

• Ferdinand Ihringer's math blog: https://blog.ihringer.org/ (formerly https://ratiobound.wordpress.com/).

• The Grammar According to West (a lot of nice advice on mathematical English writing): https://dwest.web.illinois.edu/grammar.html

• A database of interesting graphs and their properties, featuring a search by a graph drawing: https://houseofgraphs.org/

• Datasets of highly symmetric objects: https://graphsym.net/

• A simple online visual tool for working with graphs, easy to try some classic algorithms, highly recommend for those doing their first course in graph theory to play around and learn: https://graphonline.ru/

• A very nice and extensive wiki-type website devoted entirely to group theory, covers a lot of terminology, properties and classical results with proofs, and information on popular small groups: https://groupprops.subwiki.org/

• Online visual editor that can generate a tikz code of the picture: https://www.mathcha.io/editor

• Websites for drawing (visual to png/svg/tikz) and simulation of finite state automata: https://madebyevan.com/fsm/ and https://automatonsimulator.com/

• Another AI-equipped note-taking and PDF-annotating online tool, and one other free feature it has is generating Python code from a text prompt (and it's often not terrible!): https://app.avidnote.com/

• Citation generator (including but not restricted to DOI -> BibTeX): https://quillbot.com/citation-generator