[gvnonor]

Or one could simply use a ready made blog-platform like Wordpress which supports a majority of the features listed and maybe modify it a little

> Allow signup/signin

Check.

> Allow public sharing of journals/non public

Private and public posts.

> Allow submitted “ideas”

Use comments for getting those.

>Make it look decent

Thousands of free and premium themes available.

[jnoller]

Or they could use posterous, livejournal, blogger - or an internal text file. There's a million things that could do it, the idea is to make one tailored for it and tailored to the idea. Sometimes a custom built system can beat a generalized system made to "sorta do it".