Maybe not particularly useful, but I find these links quite neat :D These are not sorted right now, maybe I will do it one day.
Perpetually updating, never a final product
W3Schools - Tutorials and References on many programing
languages
Font Generator - Has a neat feature where you can draw a symbol to find the glyph of it
google-webfonts-helper - A Hassle-Free Way to Self-Host Google Fonts
HTML Color Picker - HEX, RGB, HSL and OKLCH codes
DaFont - Gallery of many different fonts made by people with various licences
Theoi Project
Perseus Digital Library
A Greek Alphabet Oracle
Sortes Homericae, more specifically Homeric
Oracle/Homeromanteion
Hellenion Attic/Athenian Calendar
Delphic Calendar
Underflow - Prayers to the Gods of Olympus
Books: (I have pdf copies of all of these, you can
email me for them :D)
Festivals of the Athenians by H. W. Parke
Hellenic Polytheism : Household Worship
WeVikings - English translations of Old Norse sources
Hearth and Field - Prayers to Heathen Gods
Old Book Illustrations
David Rumsey Map Collection
NASA Image and Video Library
Pexels - Free stock photos, royalty free images & videos
Unsplash
NYPL Digital Collection
Rijkmuseum Collection
Artvee - Public domain paintings, posters and illustrations
Online Etimology Dictionary
Online Encyclopedia of Writing Systems and Languages
Wikisource (many different langauges for many different public
domain texts)
Project Gutenberg - public domain works
Project Gutenberg Australia - public domain works
German|Deutsch:
Dict.cc - German|Deutsch-[a bunch of languages] Dictionary
Netzverb Dictionary - Conjugation/Declination of German Words
19th-Century German Stories (English&German texts)
Romanian|Română:
DexOnline - Romanian Dictionary
Delphi.tools - A collection of small, low stakes and low effort
tools
ORBIS: The Stanford Geospatial Network Model of the Roman World
Electric Zine Maker from AlienMelon
Free Online Image Editor
Squoosh - Image Resize