Way back in the Stone Age, the old Zompist Bulletin Board had a thread, visible here if you are inclined to do a bit of Internet archaeology, called "The Correspondence Library". The Library was dedicated to collecting, documenting, and discussing attested diachronics (viz. sound changes) in real languages. This was of interest to a number of conlangers because it could help inform more realistic sound changes for their own projects, but the format was poor--as a thread on an Internet bulletin board, reading and searching it were clunky operations.
It was while I was a linguistics undergrad at OU that I thought about throwing together a PDF version of the Correspondence Library. However, I wanted to add more information to it before I actually ended up releasing it. The search took a long while because everything snowballed until I suddenly had a document with a page count in the triple digits. In any case, on 26 November 2013, the first version of the Index was released.
The Index is not an academic source, nor is it perfect--far from it. The most glaring erratum in it is the presence of the Altaic section (younger me was a gullible lumper); some of the correspondences aren't strictly linear proto-to-daughterlanguage in nature; I tried converting whatever phonetic notation was in my source documents to IPA, which caused its own issues; and there are a number of other typos and inaccuracies introduced through various means such as incorrect information in the source and good ol' human error. Regardless, I have a certain fondness for historical linguistics (and also for TeX), and I poured my heart and soul into the project.
I love it when people use or build off of the Index.
I kept on expanding the Index for several years. I eventually put down the virtual pen for various reasons, including mental and physical health. The Index' reception has soured somewhat, I've noticed, and that definitely puts a damper on my drive to do anything with it…but, as I related on the homepage, I do have a mind towards resurrecting it. I'd love to get the chance to fix my mistakes (especially that Altaic section--ugh!) and add new material.