I think a calendar is very useful, but I'd also rather see a "core", simple, extensible-via-modules portal relatively quickly, then add the extra bits as modules later.
I am using phpwebsite over at www.fragfestuk.com
, but that's because I needed something fast a few weeks ago. I am following phpBB Portal avidly, as if it is anything like as good as phpBB I will be looking to switch to it.
A good, small core with a well documented
module system would work well
I am a software developer in real life (C/C++), and would like to write some modules in php for my own web site that may be of use to others.