Sorry in advance for how long winded I am probably going to get. I always do. It's literally a medical thing
First Question
Hmm, if you're looking for a unified, comprehensive resource that lists and catalogues a close-to-complete set of rules-lite small games, I don't believe one exists, but I could be mistaken. That sort of thing could be real good to have for indie games in particular, if it was well set up and truly comprehensive, but I suspect that maintaining and updating that would be a logistical nightmare - as small as this niche is in the grand scheme of things, there are still new things getting made almost every day, many of which are being made in even smaller sub-niches that someone maintaining a database may not immediately be aware of.
As far as your specific parameters (1 to 4 pages, good for one shots), if you're looking for ready made frameworks or well regarded examples, the "Honey Heist" and the "Lasers and Feelings" models are both very popular and tend to work pretty well if you're looking for something super rules-lite but not SO rules-lite that there are no rolls or dice or stats at all. There are a ton of different hacks of each of them, and they are both "systems" that explicitly encourage hacking and remixing.
Other than that, there are just SO many. I myself have written at least, like, 7 that would probably fit the criteria, and a few others that might debatably fit. And I'm a nobody with no real following or whatnot. I am sure the cup runneth over once you get into the large ocean of broader ttrpg possibilities. Doing a simple google search yields some results but those are mostly comprised of listicles with Top 5 or Top 10 lists and such.
I wouldn't even say that most of the stuff you've even listed qualifies fully. I wouldn't say Powered by the Apocalypse (PbtA) is necessarily rules-lite or small, and Forged in the Dark (FitD) is crunchy as heck (and was originally an extreme hack of PbtA anyways), and OSR is more of a broad design "philosophy" than a framework ... and nobody seems to 100% agree on what that philosophy actually IS in concrete terms ... it's one of those "I'll know it when I see it" deals, except everyone seems to know and see it in different ways and in relation to different things (not that that's a bad thing). Then you've got your other similarly vague "movements" like Lyric Games and Sworddream, and newer frameworks like Trophy and, and, and ... yeah, I can definitely see how it can be hard to comprehend and overwhelming.
My advice would be to just research and explore at your leisure based on your own interests - itch is a great place to find a lot of good small ttrpg games to quickly check out, even if its search function can be a bit fiddly at times. I'd also follow that up with the "make your own" - not in a dismissive way, but in the sense that you already know exactly what YOU like, so nothing beats a totally custom system that will 100% be what you want it to be. I definitely understand the desire to build on top of a proven framework, and that can be good fun too, and I definitely understand the desire to explore other models so that you can do yours "the right way" and that's also not a bad idea, but at the end of the day, there's not really a "right way" just a way that is "right for you."
There are also some podcasts that cover a bunch of indie stuff, and those may be a good way to get familiarized in less immediately committal way (like, you know, you can listen to them while doing something else, like driving). Personally, I would still very much recommend Modifier, hosted by Meghan Dornbrock, for a good overview. I am not sure if the podcast is currently on a hiatus (a lot of things made by small creators are due to the pandemic - since honestly just functioning has been hard these past few years) or if it's defunct, but it's backlog is still incredibly good, informative, and relevant. Meghan is a great interviewer and super open to designers of all stripes. There's even an episode with me in it (shameless).
And if you're looking for something super quick and ready to go for an upcoming session, again, I would very much recommend taking a look at Honey Heist (and its various hacks) or Lasers and Feelings (and its various hacks), since one can pretty much pick up and run them in literally minutes. I'd be happy to talk about other possibilities and give out more recommendations, of course.
Second Question
From what I can gather, the board is now pretty quiet for fairly standard reasons. Perhaps there was some drama behind the scenes that I am not aware of (there is always some kind of drama in ttrpgs, I guess), but from what I could gather, it was simply a case of too much, too soon.
I think the most enduring online communities need space to grow organically, and I think that may still someday happen for this board, or at least I still hold out hope. When itch.io announced that they were looking for input from indie tabletop game designers in how to create and structure this forum, some leading voices in the scene at the time saw this (understandably) as a great opportunity to establish a new centralized discussion hub for indie ttrpgs all across the board, a sort of unifying space outside of twitter (which, as we all know, is where most "discourse" happens these days, and which is more or less designed to be free from the pesky burdens of nuance and readability).
Prior to this, there used to be a "circle" of indie ttrpg designers on Google Plus, of all places. It was probably one of the few things that specifically thrived on that platform. I have no idea how or why this happened, as I wasn't really there for those "halcyon days" and at the end of the day that fact may well be emblematic of the core issue. While there were a lot of cool people doing and talking about a lot of cool things on Google+ in those days, it appears to me that even that group was comparatively insular, and that in the end it was more or less a large clique of friends who happened to rally around and meet based on a specific hobby. While there is nothing wrong with that inherently, it does cultivate a bit of a "cool kids table" dynamic, likely without intending to. I have been around making ttrgps for years before I even knew that group was a thing, and by the time I did, Google+ had shut down. I suspect a lot of other designers were in the same boat. The Google+ group ended up becoming something a lot of us found out about in retrospect, talked about in almost reverent tones by former members, a lot of whom then went on to be quite successful (comparatively speaking) in the "scene," especially once let's play podcasts started to really become a thing. I suppose the chronology varies for everyone, but basically a lot of newer designers (and many working in the margins) ended up "missing out" on that mythical Camelot of communication and networking.
When itch set up these forums, there was a big push, coming from industry newcomers and emerging marginalized designers, to make this the New Camelot. It was an exciting prospect, since we had all heard the stories of how great it used to be back in those Google+ days, and we all wanted a taste.
Unfortunately, I feel like we might have wanted it a bit too much. When you try to force a thing like that to happen, instead of it happening organically, it's just not likely to work out, at least in my experience. Another related issue, in my view, was that a ton of people joined and participated in the initial set-up discussions, but then the immediate influx ended up being extremely overwhelming for some, and I am sure many folks felt self conscious about actually posting and interacting if they weren't already friends with some of the other people, and so on, and so forth. The majority of the introduction posts seemed to come flooding within a very short period of time, and the pressure to "build something" was very high, too high not to cause a deflation and loss of interest amongst many participants.
And then, of course, many of the leadership figures, who may still be lurking occasionally, simply became too busy to tend to this garden very actively (and possibly too discouraged?) - some of them ended up having quite a bit of deserved success (again, comparatively speaking, whatever success means in indie terms), and moderating and promoting a forum, let alone trying to establish a culture within it that would lead to fruitful networking and exchange, likely became a very distant priority. Plus, a lot of people were already overwhelmed trying to keep up with several discord servers established to fill a similar role. Inertia sort of took over from there.
Personally, I still see the potential, but I don't want to force anything or rush anything. I asked the itch folks to set me up as moderator last year, but there isn't much to moderate usually, so I mostly just log in every few days and check to see if there is new spam than needs removing. Occasionally there's a post like yours or a new intro. I did try to promote the forum again back then, and we did get some interest and discussion going, but in the end it was like three people, myself included, arguing over whether or not ttrpg discourse can ever not get heated. It got a bit heated. But it was literally like one thread.
At this point me and the other mods who check in occasionally are mostly just holding and maintaining the space and hoping that it can have a chance to become something at some point. I think expecting it to be the New Big Thing is not the most productive thing, and likely contributed to it being something close to a ghost town, so I personally hope it's allowed to slowly evolve in time. Who knows?