OSR (Old school revival) is an interesting movement in tabletop RPGs world. If I understand correctly, the idea is to focus on believable and interesting action rather than crunchy numbers and balance, making easy to generate adventures on-the-fly:
+ https://en.wikipedia.org/wiki/Old_School_Revival
+ https://www.reddit.com/r/rpg/comments/7a8kqm/

Stars without number is an OSR RPG in spaaaace:
+ https://youtu.be/lVTu69Usu2Q
+ https://youtu.be/ZyAMLPj4N0o

List of retroclones (osr rpgs)
https://1d4chan.org/wiki/Retroclone

The main issue most of settings have with races is that they are still created by humans and so inspired by real nations or psychotypes. And it has a good reasoning, especially for playable races. A human is unlikely to properly roleplay a believable alien.

It would be not a big deal but there is one detail that exposes the issue, making the whole conception look artificial. Humans are defined as "the most versatile race", they can have any class, stats, skin color, while all other races are limited.

A possible solution I see is to reshape humans as well or just get rid of them. It's a fantasy world common, you can do anything you want, why play humans? And for sci-fi setting it even can have a good explanation, either that all nations mixed in one (with one language and one pale skin color because there is no sun anymore) or other nations are just extinguished. And here you go, everyone is on the same level, no universal races, no intersections.

"Stars without number" races a similar concern about humans unable to roleplay aliens. The solution is more boring, though. They just made humans the only playable race by default.

Generator of everything, from names to quests:
https://donjon.bin.sh/

A few good generators for "stars without number":

+ https://sectorswithoutnumber.com/ (source!)
+ https://www.orffenspace.com/swn/swn-toolbox/
+ https://www.orffenspace.com/swn/starship-generator/
+ https://swn.emichron.com/
+ https://perchance.org/swn-world-generator

Unofficial character sheets for "stars without number" adjusted for classes.

Source: https://www.reddit.com/r/SWN/comments/6xa96m/

About DnD 4e:
https://youtu.be/cpmUxfS4LF8

The most played race+class is human fighter:
https://youtu.be/-J6OlsTSxRc
🤷‍♀

Free adventures for traveller sci-fi ttrpg:
http://www.freelancetraveller.com/features/advents/index.html

There is a list of reasons why I decided to give a try to OSR games after DnD 5e, Pathfinder 2e, Starfinder. I will talk mostly about Stars Without Number (SWN) assuming that other OSR games provide a similar experience. Also, I know a few games like Call of Cthulhu that cover some of the points (not all of them, though), so you can read the main point as "try something else, not only DnD 5e".

1. It is sandbox-oriented. Your players decided to go into another city or make a turn that you didn't expect them to make, and now it's time to improvise. It is the hardest part of the game and it will inevitably happen. Most of the systems and scenarios leave you on your own. SWN gives you tables to quickly generate anything, from star sectors and adventures to NPCs and rooms.

2. The combat is fast and dangerous. "So, it is your turn. What are you doing?" - "Hmmm... I... I attack the closest enemy with my sword". DnD 3e+ and clones make the combat slow and repetitive. You punch enemies until they die. Sometimes, you cast a spell, usually to damage an enemy or to heal a friend. There are some fun spells but most of the fighting is still punching. SWN (and Cyberpunk games) makes the combat fast and dangerous.

3. Characters can die from one bullet. It is a bit of repetition of the previous point because it's worth emphasizing. If you don't want your character to die, you play smart. When you think and find alternative solutions, it makes the game much more interesting compare to when you just stub everything until death.

4. Fewer dices to roll. The system is secondary. Roleplay comes first. When a character does something usual, like a mechanic fixes an engine they know everything about, you don't roll. They just succeed. A small change making a big impact.

5. Supports snap decision. So, a character jumps over a pit. What is the difficulty check? Well, Pathfinder provides a separate table for every pit size. And don't forget weather conditions and the slope angle. SWN says: "Should it be a difficult check? Well, then it is 8". Instead of turning pages and making math, the game tells you a simple easy-to-remember algorithm.

6. Everything is in one book. It's better for budget, for getting started, for everything. I felt helpless having only the Pathfinder core rulebook, I had no idea how to make NPCs or monsters, so I opened a bestiary PDF, and then the world guide, and then a separate book about deities... SWN is in one book that just works.

7. Easy to learn. A few simple rules, a one-page cheatsheet, a small character sheet, and you're all set. Wanna magic? Here, a few pages of all spells, all are powerful and unique. You can create your first character in an hour or less. In Pathfinder, you'd better plan a separate session for it.

8. Easy to get started. Again, related to the previous point. SWN provides only 3 classes (and multiclass for them), a few pages of backgrounds, a few pages of focuses. While in Pathfinder players one session learn about the class they picked, SWN in the first hour allows them to learn every available option. Oh, and also any class can do anything.

9. Attributes are rolled. You don't pick numbers, you roll them. I know, it sounded stupid to me at first but then I got the idea and started to like it. A bad Strength score can't stop you from being a Warrior. First of all, play smart. Second, scores from 8 to 13 all give the same 0 modifier, and so it doesn't really matter. On the other hand, tolled attributes make you learn how to adapt to what you have (like in the real-life) and make the character creation even faster.

1/2

10. Let's talk about treasures and experience points. DnD expects me to constantly reward players. Killed a bunch of goblins? Great, you find a magic sword of storm in their pile of trash! Why is it here? Hell I know! But it's better to be here because soon the module has a powerful monster that is immune to a non-magic weapon. And if you're going to replace the monster, by what then? More goblins? And yeah, don't forget a bunch of exp for everything, they'd better scale. SWN makes a smaller gap between armor classes and weapons damages, there is almost no immunity (well, if you don't try to kill a soldier in a power armor with a stick, of course), and exp is given for milestones (you reach the second level at 3 XP).

11. Balanced. Over these 3 classes and all focuses, all are helpful, needed, and do better different things. In the DnD world, on the other hand, everyone always talks about "overpowered" or "useless" spells, classes, items. And the issue not with the balance itself but with that it matters.

12. Uses probabilities. DnD uses d20 for everything. OSR is 2d6 for skill checks, 1d20 for attacks. So, in combat, when you have to react fast and anything can happen, you have a long even distribution, while in a calm environment when you can rely on your skill you have a smaller normal distribution. One more small addition making a big difference.

2/2

A bit related rant in support of points about the balance and fights:
https://www.youtube.com/watch?v=SzlR00IZ29A

Searching "overpowered" in r/dnd or r/Pathfinder2e gives too many results to count:
+ https://www.reddit.com/r/DnD/search?q=overpowered&restrict_sr=1
+ https://www.reddit.com/r/Pathfinder2e/search?q=overpowered&restrict_sr=1

It's unfair to compare it with SWN because of much smaller popularity but for the record there is only one result for SWN with "overpowered" in the title. And the top answer from the game creator that it is different in the Revised edition:
https://www.reddit.com/r/SWN/comments/79bp8x/

3/2

ToDo: turn it into a text because YouTube blocks copy/paste on mobile version :/

Cheat sheets for Stars Without Number:
https://drive.google.com/drive/folders/1DiYjWulYeTB_UDua-J-FxMNsoCKTgfK9

downloaded, just in case

Amazing generator of narrative description of locations, buildings, npcs:
https://eigengrausgenerator.com/

This is amazing:
https://youtube.com/playlist?list=PLlUk42GiU2guNzWBzxn7hs8MaV7ELLCP_
It starts from how to run the first game and proceeds to all related topics, like improvisation and alignment.