…hello folks…im curious to know, how many community projects in past happened, and finished ?
Zero afaik. Thing is most people are mainly about implementing their own ideas. Even for coding most people want to implement stuff their own way, even right down to code formatting. That is also a reason why good contributions to the engine are so hard to realize - most extensive code has to be rewritten to fit into the engine paradigms, making the overhead almost as big as when a core dev implements it himself. Or the feedback to developers causes so much friction that they give up the implementation.
Both is understandable, if you wanted to realize somebody elses ideas or do code in somebody elses way you could just as well work at a software company and earn some money with it 
The idea is nice…
Imagine this as an art project:
Every day someone adds only one line to a game (must compile and produce interesting gameplay).
Lines must not exceed 100 characters but there is no coding convention other than camel case.
Alternatively a texture or 3d model can be uploaded (must be under CC0 and author is the uploader).
Have some people share one github repo and see what’s resulting.
Most certainly a Frankenstein-Monster will result - but who knows… 
I think both answers so far have assumed you meant a community game project. You may want to clarify what kind of ‘community project’ you mean if that’s not the case.
Else there are quite a few successful community projects… just not games, necessarily. For all of the reasons stated.
People often don’t realize that managing a handful of people is a full time job. That doesn’t leave much time for coding for that person, even assuming the group accepts the leadership. Most of us are here to code and so will find a balance where we get to keep doing that.
By the way - I was talking serious.
I don’t know if such an art project existed before or if jmonkey folks would be the first - we would be real art pioneers (and art is mainly about being the first one who ever did this).
Also, it would be extremely cool if that project went on forever and ended up as the greatest MMO of all times or as a collection of one million mini games.
@erlend_sh - what do you think?
Ugh, tell me about it. Being a coordinator and a programmer has taken it’s toll on me.
I would love to see something like this. We should totally do something like this.
I think it’s a pretty novel idea. I don’t have the bandwidth to manage it as an official jME project though. But if you wanna try round up some people, go nuts! 