Kind of surprised Basecamp from 37Signals hasn't come up in the discussion, or ActiveCollab. I use and love ActiveCollab, and I've set it up for a couple of contractors.
They both work much in the same way forums do, but more robust. Time tracking, messaging, invoicing, file sharing, email support. Plus it helps to keep everybody on the same page.
Let's you define permissions so that you can grant access to clients who may not be on the job site everyday, still keeping them apprised of the work but not letting them see the internal talk of the company.
A GC I set it up for recently uses it to keep track of multiple projects without having to drive around to them every day. The foreman uploads pics and details of the days work, and the boss makes weekly visits instead of daily to make sure his money is staying green.
Pretty cool stuff, be glad to answer any questions about ActiveCollab. Only used Basecamp for a little while, wasn't a fan of the monthly fees.
Re-reading to edit and I realized it sounded a little.....company spokesman. I should mention I have no affiliation with either of the companies, other than I use their products.
That is all
