don't overthink it, post what you want.  Ask forgiveness, not permission, and I bet the folks at hackaday would agree with that approach.

tl;dr  just tell me what i can post and what i cannot ;)

Not particular stuff yet, but I have some ideas for projects, and some things might not be very 'hacky', just making things not related to electronics.
I just started thinking about it some more,  and it just gets more complicated.  I like metalworking, and that's something i don't see a lot around here, so lets consider the list below.  If you do stuff in the list from top to bottom, when would it be appropriate to start posting it here?

1)  Buying or having a lathe 
1b) Making a simple object on this machine, like a spinning top 
2) Adding a tool bought at a store to this machine
2b) Making the same spinning top on this lathe using the tool
3) Adding a tool, not intended for this machine, bought at a store, having to make it fit
3b) Making the same spinning top on this lathe using the modified tool
4) Making a larger project with the lathe
5) Converting the machine to CNC
5b) Making the same spinning top on the converted machine
6) Sharing the digital designs for the spinning top
7) Optimising some performance characteristics of the spinning top

What comes to mind:

1 and 1b not that interesting, but i like making spinning tops and maybe i want to share them, but they are 'low tech'
2 and 2b see 1
3 is technically a hack so i think that's ok 
3b is the same as 2b and 1b, but now it's the product made with a hack, is it more interesting?
4 When is a project something to show? I can make an intricate design for a candle holder, or parts for steps 5
5 Is interesting, especially if you design the electronic yourself, but there are sites dedicated to CNC machines, like cnc-zone.com. 
5b It's still just the same round piece of metal, but now the product of a larger project
6 Is nice to show, but also something for sites like thingyverse
7 Is interesting, 

Now what if someone else wants to optimise and make perfect spinning tops, but doesn't have a lathe or knows how to operate one? He creates a project and starts with step 1. Now buying a lathe is a project milestone.

I thought up 3 other examples in a short time, but i'll leave them for now.

once you are sharing, its good.  If people don't like it, they will not look at it... You can put it on cnc zone, thingyverse & hackaday .....& you tube & anywhere else....Is there already open source spinning tops? .. Maybe you could be the first.. ?  If there is an open source one, you can always try to make a better one...  No doubt the hackaday community can then add some electronics & turn it into a flying saucer...

it's not about the tops in particular that was just an example. Although i just checked, and someone kickstartered 130,000 USD for some very pretty ones. :D

I say post whatever you're working on; if people don't like it, they'll just not follow it. Hell, one of my projects just documents taking something apart. Post, share, etc--worst thing you'll hear is crickets.

sounds like one big project with many cool and interesting logs! 

After getting really annoyed by some posts that claim "the HAD prize is unfair, because I can't participate" (for their own personal various reasons) I started thinking about different types of entries and whether they would be accepted.

Some people complain that the prize is unfair because they don't have money to put into it. Despite the fact that most prizes that I know of (including mine) are under $100 in development costs. So I was trying to come up with entries that required NO cost.

Would a software-only entry be acceptable? I think so. If someone made a good library of functions for one of the micros, if someone duplicated the Arduino IDE and bootloader for a different processor, if someone had an interface library to a bunch of IOT commercial products, then yeah... I think that would fly on Hackaday.io and probably as a contest entry.

Then I mentally thumbed through C.L.Strong's book "The Amateur Scientist". Would an entry detailing how to make a population study in the local woods (of insects, or plants) and how to write it up for publication be acceptable?

There's a rock overhang in the woods near where I live, it's perfect for taking shelter from the rain when you're hunting. Could someone do an archaeology dig there and find Indian artifacts dating from 5,000 years ago? If they took campfire coal samples and determined the age from the magnetic direction, then that would probably fly also.

That same overhang has a ledge in the middle that's got plant life growing out of it. That's an isolated ecosystem - would a study of the plant/insect/animal life from that ledge fly on Hackaday.io?

I remember someone building a half-submerged game stand in a pond. You could see out over the pond, but since the floor was below water level you could see underwater as well. They made lots of observations about the plant and animal life in the pond during the course of a year. Would a submerged observation construction be acceptable? I think so.

How about Astronomy? Lots of people have made their own telescopes, and some have made their own mirrors. You can build a really nice scope out of plywood and if you're clever you can even cast your own mirror.

I know someone online who modifies microwave ovens (that he gets from the dump) to do plasma experiments using microwaves.

Gah! Don't get me started. Combination of OCD and high passion.

I think the Hackaday people are dead-set against censorship in any way, so I suspect they wouldn't mind *any* project that would otherwise be legal.

Maybe Hackaday should post a quick challenge: "Describe a potential HAD prize entry that requires *no* cash outlay".

You might get some interesting responses.

I do not think the prize has got anything to do with this?.. The prize seems to be limited to a few topics.(pollution, food, energy).  I think this .stack is just asking about the scope of hackaday, not the scope of the prize??..  A proper hacker would get over the 'no cash outlay' very easily by saying he/she got all the parts free at the local dump, as scrap from his office etc..

MW motors is right, I wasn't talking about the prize in particular. I haven't put much thought into the Hackaday prize because what I'm currently working on only fixes the I don't have a *What i'm currently working on problem, and that doesn't count does it?

But I think you'll be up to speed quite fast if you read my other reply ;)

Hackers are self-motivated, and learn through experimentation and persistence, as opposed to through "traditional" means.  With that in mind, post any project you like..  It does not have to have electronics. If you read 

http://hackaday.com/about/

It states.....

We are taking back the term "Hacking" which has been soured in the
public mind. Hacking is an art form that uses something in a way in
which it was not originally intended. This highly creative activity can
be highly technical, simply clever, or both. Hackers bask in the glory
of building it instead of buying it, repairing it rather than trashing
it, and raiding their junk bins for new projects every time they can
steal a few moments away.

Anything particular you want to add but are unsure about?