chorsley

I've been using TiddlyWiki for some months successfully:

http://www.tiddlywiki.com/

Very simple (single HTML file, web server not required), local, lightweight, can sync with Dropbox easily.

For teams, we're heavily using the Open Source version of Etherpad. Not a wiki, but a great collaborative text editor.

Even cheaper hack: two logins. I have one account for projects, one for play. On my project account, I run Self Control (http://visitsteve.com/work/selfcontrol/) to block distractions (now experimenting with Concentrate: http://getconcentrating.com/). I find just having two differently configured environments is a good cue which sets me in my work groove.