I can’t improve on Christopher Culver’s description at Безѹмниѥ, where I found this link, so I’ll just quote it:
Cyril Babaev… has written a historical grammar of Lithuanian with some interesting comments on Lithuanian’s evolution from Proto-Indo-European. Babaev’s Indo-European Database contains links to other grammars. It is probably the most useful site ever hosted at a Bizland.com address.
I find by googling that Babaev, who is not a linguist by profession, has also done a similar grammar of Old English. I should add that Bridget in Christopher’s comments says “I’m not sure I trust the IE Database site. I was just looking at Hittite & Lycian and noticed 3 or 4 things that are either just plain wrong or disputed at best.” Since it’s a hobby for Babaev, I guess that’s only to be expected.