I was asked to do this as a favor to a GM who has hosted a lot games I've enjoyed.  He wanted to play in a game -- a sentiment that I understand completely -- although I am not sure my doing this is a fair exchange for him.

My sentiments are best expressed with my response to him, which appears below (lightly edited).
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BUT -- be warned.  I can almost guarantee that your experience will suck.  There's a reason I haven't GM'd in 40 years.  I lack the creativity to create an immersive world, much less one as in-depth or even organized as most players expect/desire.  I am too laid back to hold players' feet to the fire.

I recognize, and try to heed, my limitations: I can't dribble a basketball with my left hand, I can't jog or run for a long time without purpose, I can't draw, and I can't GM.  I simply can't.  So I don't do those things.

And I genuinely fear that trying could fail so spectacularly that friendships are impaired.

So . . . if that dire warning does not dissuade you or dampen your enthusiasm, here's what I could take a stab at:

At least initially, and probably forever, the game would not be open to the public.  It's [just] you [two].  To make the numbers better I can invite my friend who played for a bit in Gods Reborn; he was the ranger who had to drop out due to RL issues.  He and I go way back.  That's up to you [two].  And I would throw in an NPC to cover any necessary role(s) that the players don't.  This may make scaling for the small number a challenge, but I prefer that "problem" over opening it up to a huge crowd.  (Scaling is always a problem for me anyway; I never know how many ogres a party should be able to handle.)  At any rate, three PCs and an NPC would cover the archetypes.

I have no "system" so would probably steal one of your variations.  I have no adventures or worlds except . . . years ago, I obtained some modules because I thought my younger son might be interested.  Some are the classics, some are from obscure publishers.  I would have to figure out whether I just want to do a series of one-off adventures or put it in a pre-packaged world.  I'd need a bit of time to figure that out (and do a lot of reading).

And then there's figuring out how to do it RPoL.  It may be a situation where I pester you with "how do I . . . ?"  questions.

And one last time, because it can't be emphasized enough: I really suck at this.
This message was last edited by the GM at 23:49, Sat 19 Feb 2022.

Consistent with the above sentiments -- particularly the one summarized as "I don't know exactly what the hell I'm doing," I will not have rules for everything right off the bat.  I have (with grateful permission) borrowed extensively from the aforementioned GM.  However, I did not want to borrow things that I did not fully understand or had no experience with.  So, those familiar with his rules, the absence of any does not necessarily mean I disapprove of them or have anything particular in mind.

Also consistent with the above, there is no "world" as such.  It also won't be original.  It may be a series of disconnected modules (ranging from the classics to the obscure) that may end up getting tied to a city as a home base.  But there is no "stop the destruction of the universe" plot in place.

In other words: it's a sandbox!

We're here to have fun, not sweat the finer details.

And given the special purpose for this game's existence -- if it's not what you want, say something.

All suggestions are welcome and appreciated.
This message was last edited by the GM at 13:17, Mon 28 Feb 2022.