Dr. John van Wyhe has been on a mission for years now to collect and make available the text of Darwin’s work online. The web site has been up for at least a couple of years, but now apparently has attracted the attention of Nature, so there is now a bit of a buzz. One thing that looks new-ish on the site, or at least I overlooked it before, is the availability of 2nd through 5th editions of the Origin of Species. Something that has been a long-term idea of mine is to produce a variorum of OoS, and now there is at least a resource to get the text of all versions from. There is another site that has a list of Darwin’s correspondence, but last I checked, they simply allow a search on an index, and do not provide the actual text of the correspondence.
So far as I can tell, no one has published an algorithm for production of a variorum version of three or more source works. This is in itself a neat little problem to work out. Certainly, if I do fit that in somewhere, I’ll get in touch with Dr. Wyhe to contribute something back to his project.