Mythic GME 2e provides a lot of tools out of the box. It's one of those things that you could take a couple concepts from it and improve the experience of your solo, collaborative, or GM-driven game. It would even be a great source for writing, in my opinion.

A few examples:

• The Fate Chart and optional Chaos Factor, for guiding outcomes, and ratcheting up the tension in a natural way
• Lots of genre-agnostic and system-agnostic charts for NPC responses and event outcomes
• Threads, Characters, and Scenes for tracking story and lore details in an organized way, as well as how to "roll against" them to come up with new plotlines

There's a lot more. I recommend skimming through it once, and picking a couple elements to work with, then tweaking gradually.

If you're on the fence, check out the One-Page Mythic Game Master Emulator by the same author. It's also extremely useful and enough for many solo players and GMs. But I imagine your interest will be picqued enough to check out its bigger sibling.

Although I have a soft spot for CRGE/UNE/BOLD, I think Mythic may be more accessible for the typical player or GM.

Every Quill game is fantastic, and this might be my favorite one. I was playing Quill while working on a separate songwriting project, and it really helped me get past some creative blocks, especially when I was writing more romantic sort of songs.

The framework Quill provides is light enough that you don't have to constantly think or look up the rules, but it provides enough constraint and open-ended detail, that it helps get the creative gears turning. The scoring system is quite clever as well!

One Page Solo Engine was my first oracle, and it's excellent for coming up with NPC motivations and other things that would come up in a solo game. However, it would also be excellent as a quick first go-to Oracle for a traditional DM as well.

Pair it with Cairn, Knave, or other light OSR game, and you have all you need for loosely-directed RP.

If you eventually find you'd like slightly meatier:

• There is the One Page Mythic GME (and it's bigger sibling, the Mythic GME 2e), or
• CRGE, UNE, and BOLD, by the late Zach Best of Conjecture Games, which can help come up with entire plots, waylays, and involved NPC interactions

Cairn is my go-to for a beginner-friendly D&D-like fantasy experience. It lends itself to solo, collaborative, or GM-driven gameplay. The core rules fit on just a few pages, and I found that players with a little bit of D&D knowledge picked it up no problem. It's easy to adapt scenarios for other systems to use Cairn.

It's very playable as is, with very little preparation, but it's also extremely adaptable as well.

I feel like it would also work well with a hex crawl adventure or a West Marches-style campaign with little effort, although I tend to run more focused scenarios.

If you like Cairn, you may like some of its descendants and relatives:

• Grave (a dark fantasy OSR with some Souls-like mechanics such as bonfires, an interesting alternative to permadeath while keeping a dark tone)
• Knave is very similar to Cairn but is classless, and is streamlined in someways and crunchier in others
• Monolith is, imo, the best science fiction OSR-like game out there. I am running the Gradient Descent campaign currently using Monolith, and my players are having a blast.