Wikis are great not only to co-author documents, but also to implement private or public knowledge bases. For CommunitySense, I wanted to install a number of wikis. Two issues arose: which wiki and to have it hosted somewhere else or host it myself?
The quest for the right wiki took me quite a while. A good starting point for comparing the features of the many wikis around is the WikiMatrix. I tried quite a few of the wikis listed, but none of them served all the purposes I intend to use the range of wikis for (co-authoring, file management, personal information management, etc). One option would have been to use different wikis for different purposes, but the learning curves and maddening variations in syntax caused me to make the principled decision to focus on one wiki only and master it well. I chose MediaWiki, as it has the most complete set of features and has proven to be very reliable and , as demonstrated by its use in Wikipedia. It also has a large user base, guaranteeing sustainability and further development.
The next question was whether to use a hosted version or host it myself? Hosted versions are expensive, especially when hosting multiple wiki instances. My current Dutch provider, Hosting2Go, didn’t provide good support for MediaWiki installation and configuration. In my quest for another provider, I came across SiteGround. They not only provide great web space (750 Gb!) and bandwidth (7500 Gb / month!), but their customer service also installs as many MediaWikis as you need. This for only about US$ 6,- / month. I had three MediaWikis installed, all of them ready for use within 15 minutes after my requests.
After their installation, I only had to make some small changes to the LocalSettings.php configuration file, in order to get the right privacy settings. This turned out to be really simple with the help of the following document: How to make your MediaWiki private?
Making CommunitySense 
I found your blog on google and read a few of your other posts. I just added you to my Google News Reader. Keep up the good work. Look forward to reading more from you in the future.
Unfortunately, the performance of SiteGround has become very unpredictable in the past few months. I am now moving my applications to another provider. I can thus no longer recommend this provider.