How we might count the number of users of TiddlyWiki is an interesting question, and it is often asked. My personal response is that it is impossible to directly track TiddlyWiki usage without compromising it with code and infrastructure that serves no other purpose than usage tracking. I regard the untrackability of TiddlyWiki as a fabulously useful property, and wouldn't change it even if I could.
Of course, there are specific usages of TiddlyWiki that can or could be tracked:
* The Google Groups data that Josiah referenced
*
tiddlywiki.com runs Google Analytics (the screenshot below shows a summary of the data for the last year)
* TiddlyFox usage stats (before the apocalypse, I believe it was running at about 40,000 active users)
* Online services like TiddlySpot can in principal include complete tracking/surveillance of all usage
* Published TiddlyWiki HTML files could be discovered and counted with a web crawler
* GitHub provides some stats about the project (eg, we're just under 3,000 stars at the moment)
But I don't think any of those could ever give us really definitive numbers. One of the unexpected consequences of distributing software through open source is that the vast majority of users are invisible: if they don't ask a question, or raise an issue, or otherwise actively interact with the community, then we simply don't see them. I visualise TiddlyWiki as a vast shop (like Ikea) but with the curious property that the happy customers are invisible, and one can only see the ones that are unhappy or want attention. It's weird, but highly efficient.
Best wishes
Jeremy