The enterprise collboaration and content management space is a crowded one. Depending on what you want to empower your workers to do, you can look at anything from basic wikis to Microsoft SharePoint to Atlassian's Confluence - to name just a few of the choices. Cyn.in, which until recently had focused on a SAAS approach to providing this functionality, has recently launched its version 2.0 - and now it's available as open source as well.
Cyn.in supports quite a few different use scenarios: it includes user management and security, collaborative workspaces, content management, blogs, wikis, link-sharing, discussion boards, and more. You can get cyn.in several different ways: as a hosted service starting at $249 per month in smaller installations, as an appliance starting at $1950 annually - or as an open-source (GPL V3) "community edition" that you can download free from their SourceForge site.
It's easy to see this as a smart move in a sector where the average IT department has too many choices: by lowering the cost of trying cyn.in, they increase their chance of actually gaining some attention. And they've made it even easier by offering a choice of downloads - you can grab and build the source, or you can simply download and use a VMware image of the running software.
But, as it happens, cyn.in doesn't have a lot of choice about making the source available, now that they're selling an appliance-based version. Crack the source code archive open, and you'll discover that it is "based on" the open-source plone content management system. Though there is definitely much value added by cyn.in's own development, it's entangled enough with plone that shipping source is certainly their safest legal alternative.