The big differences are the site's focus, how they are changed, and their scope.
The focus of niles.org seems to be announcing things to the public. The focus of Niles Community is to assist the communities as they do these things, to be a place where members of the community communicate and collaborate.
How information changes is very differrent between the sites. With niles.org, you send a request to an email address. The request is reviewed to see if it is consistent with the positions of a particular organization (the Niles Main Street Association), and if approved it is sent to webmasters to be done. With Niles Community a member of a section simply logs in, clicks a pencil icon, and makes the change.
The scope of niles.org is limited to that of the Niles Main Street Association although they often post announcements as a courtesy. Niles Community is not so limited and welcomes all that make Niles a community, including residential communities, political communities, or just folks who see each other on the trail.