Hello Mark, for now I don't try to discover frequently, and usually prefer creating plugins (perhaps sometimes prior research could help, though), but if I have to search, I have at least
the snapshot of the old Customize tiddlyspace (many links are broken, but once you know what plugin to look for, it's much easier to find it on Github or something). Theoretically, ExtensionsExplorerPlugin should help with that, but it hasn't reached that point yet in terms of functionality, should be able to search and should index many extensions (ideally, all of them) for that. Sam did some nice job for the second part (see
the thread, in fact his index may be helpful by itself), but I haven't reviewed it and haven't implemented search yet.