A few good examples:
+ https://youtu.be/MXW0bx_Ooq4
+ https://youtu.be/aW2LvQUcwqc

What happened in 80's:
http://www.thepeoplehistory.com/1980s.html
Handy if you're about to run a game in this time.

A book about how aliens and alien worlds could look like:
http://www.xenology.info/Xeno.htm

Funny lotr art:
http://www.corblok.com/

Constructor of random generators and a huge collection of existing ones:
https://perchance.org/welcome
There is no sorting or convenient search, so it's hard to find good ones. But there are good ones. Their subreddit has some links:
https://www.reddit.com/r/perchance

A nice constructor of the character appearance, with pixel art items:
https://reroll.co/
Also, character sheet manager for DnD 5e. The free version art is very limited, though, and premium is a little expensive. However, it still can be a good inventory manager.

An interesting free PnP board game:
https://pearlyn.itch.io/shelter
Speaking of PnP, I print a lot of games. I think the best PnP you can legally download is Love Letter. Just a few cards and a very interesting and simple game. Well, the official download requires registration but you can find it somewhere else. Or download a redesign from BGG.

Ro is a constructed language to make it easy to construct and understand new words.
https://en.m.wikipedia.org/wiki/Ro_language

Just have a look at the dictionary:
https://sorabji.com/r/ro/

A video about making different interesting voices for your DnD characters:
http://www.vocabilities.com/100-voices.html
Basically, it covers what parameters each voice may have and how to mix it.

Kevin Crawford, the author of Stars Without Number, published very good rules for cybernetic implants:
https://drive.google.com/file/d/1ksvJGmYGvJGIFD9cUaW5AO05tIhrVAMy/view?usp=sharing

Cybernetics were one of a few things I felt should be better, and now they are perfect. The only things left that I house rule on top of SWN are:
1. Space battles in mechanics of FTL to be more strategic.
2. Hacking in mechanics of Cyberpunk Red to be more like a funhouse dungeon.

The Traveller RPG has an (in)famous system for generating (rolling for) random backstory events that formed your character. Players either love or hate it. Love because it's a great framework for building an interesting and alive character with a detailed enough backstory. And hate because that's the (only?) system that can leave you character without a limb or even dead before the game even started.

I just learned that Kevin Crawford published a similar "lifepath characters" framework for SWN:
https://www.drivethrurpg.com/product/154238/The-Sandbox-2

They require registration to download the file. Here, I got you covered.

Online character sheet for SWN:
https://www.swnfreebooter.net/

BoardGameGeek isn't quite good for managing and sharing your collection of games. I found something with a bit better UI and filters:
https://kallax.io/

Here is my collection, for example:
https://kallax.io/profile/BZ10S

Still not perfect, though. Would be great to add notes, like in BGG.

Some links related to the Sherlock Holmes board game. Quite useful for playing online.

+ Audio version of intros for each case: https://www.spacecowboys.fr/the-thames-murders
+ Directory, map, and Case 3: https://drive.google.com/drive/folders/1LfejFl6kqaEPZ3VIyZLczjRtowYcB8Xu
+ PDF for old cases: https://wren08.wordpress.com/other-projects/sherlock-holmes-consulting-detective-game/

Non-transitive dice:
https://singingbanana.com/dice/article.htm

I wonder if that can build a 4x game on top of it, that makes an interesting probabilistic rock-paper-scissors mechanic. Try making such dice and use them for resolving battles to spice up your next Diplomacy game.

Lots of cool magical items for dnd, each with an amazing art and description:
https://www.reddit.com/r/TheGriffonsSaddlebag