There are many web applications available that try to support online collaboration. I have been involved for several years in building and maintaining one system that was originally in PHP and was migrated to Rails, and is currently stuck at Rails 1.0, while the Rails world has moved on, most recently to Rails 2.3.
Over time I have become aware of many other systems such as Plone, Drupal and hosted services like basecamp and huddle. I often draw a parallel as follows:
PHP -> Zend -> Drupal
Ruby -> Rails -> Radiant
Python -> Zope -> Plone
Where at the base we have a programming language, next we have a framework that makes it easy to produce web applications in that particular language, and then finally we have systems that run as complete content management system (CMS) out of the box, support some basic funcationality like login, wikis etc., and also support the addition of extra functionality through some plugin framework.
Of course the picture is not as simple as this model in that firstly I don't think that Drupal runs on Zend (although there is a zend module for Drupal), and there are many frameworks for each language and many CMSs for each language and framework. However the named elements in the above schema are ones that have become close to the defacto standard in their bracket, and it is instructive to think about the pros and cons of setting up a CMS or collaboration system using each.
Writing something from scratch in PHP, Ruby, Python or other language is really a hell of a lot of work and you will be maintaining it yourself, and it will be difficult to get open source community traction given the other existing frameworks written in those languages, so really the options are pick a framework, or pick a CMS. Picking a CMS means less up front work and potentially getting support from the community associated with it, but the particular CMS may not match your current needs. Fortunately these systems can be extended through plugins, but if the underlying system is not a good match you'll have trouble. Working directly in the frameworks to make your own application give you a lot of flexibility but there tends to be a lot of re-inventing the wheel through making things like password reset functionality, which you will then have to maintain. One interesting possibility here is to incorporate a framework like google connect or facebook connect:
or even to go for, potentially closed source, alternatives like basecamp or huddle. Interestingly huddle is now available through LinkedIn and Facebook. http://www.linkedin.com/static?key=developers_widgets
and there are interesting possibilities for using twitter
Alternatives to basecamp according to http://www.slideshare.net/carsonified/cheaponomics include
http://www.goplan.info and there is an even bigger list here: http://www.whybasecampsux.org/#alternatives
Using a hosted service leaves you at the mercy of the hosted service, and so it is tempting to set up an existing CMS, but these require maintenance too, however with plugin frameworks they do allow a degree of customization. To get more flexibility one can build in a framework like rails, but as I have found out the real challenge there is keeping things up to date, which is not as simple as it sounds. In our project we stuck with Rails 1.0 in order to keep pushing features out and avoid having to spend time adapting to a changing codebase, but we built up a lot of technical debt in the process, and maintaining our Rails 1.0 is now a big handicap. Also the lack of a pluggable framework means that involving other coders is messy, although that said I haven't really experimented with the pluggable systems enough to correctly analyze the associated pitfalls.
Anyway, so this is a rather incoherent post, but I wanted to collect together my thoughts and associated links on one page ...