For a couple of projects I'm working on it's nice to have 'scratchpad' type area where information can be quickly written and accessed. A wiki is perfect for this type of information because it can be easily uploaded and modified by people working on the project WITHOUT a need to purchase an horrendously expensive server and a copy of or .
GTDTiddly Wiki has some very nice features - It doesn't need to be installed as it's just an index.html file. Java is needed to add in the functionality but beyond that there is no server side configuration needed. I've not yet unleashed any of the three wiki's I have created on a server.