In a comment on another post, Barry points me to TiddlyWiki. This is an interesting implementation: it’s very ajaxy and opens entries in the current page, in the context of the other entries you’ve already opened. Furthermore, all the data and code lives in a single html file that you access directly with your browser: there is no server or other software, so this is a very convenient PersonalWiki approach. Put it on a key for mobility. And here’s a clever feature: edit functionality is present when browsing via file:// but degrades to view-only with http://.
Barry also points out GTD TiddlyWiki, which is an excellent illustration of wiki-as-framework. This can serve as an easy entry into GTD, as it is a basic, illustrating implementation that can then be further modified to suit. It’s open source, and clear text on disk using basic, standard web technologies; very geek-friendly. It’s very light entry — if you’re at all interested, I encourage you to save either wiki file and start playing with it. Or save both, and look how the one was used to make the other — whether or not you call this 2.0 mashup, it’s a compelling approach to making apps.
Finally, Barry has documented something he calls PocketGTD, which gives PocketMod-like printouts of GTD TiddlyWiki. I haven’t tried it, but having GTD actions printed out in a nice, fold-up pocket booklet sounds really excellent, covering a real-world gap for those of us with nearly entirely digital GTD implementations. At first glance these things don’t fit well with my current GTD, PersonalWiki and MultipleDesktop implementations, but some of these features are compelling enough that I’m looking for how to integrate them.