I would like to hear ideas regarding how best to keep track of multiple installations of XOOPS. I have graduated to the level of just enough knowledge to be dangerous and find myself with multiple sites at various stages of development and upgrade.

My fault and my mess to sort out but to avoid a repeat performance, I would like to know the best way to track what actions have been taken on a site. What upgrades have been applied, what hacks, modifications etc.

Is there a best practice, a XOOPS module that I don't know about?

Is maintaining a changelog text file in the root folder a good idea?

Personally (and I doubt this is the most efficient way) I make a back up of each site immediately before making any hacks.
I then copy and rename any files I'm going to hack (add old to the file name) and put them in a 'todays hacks' folder along with the properly named and 'hacked' files once they're done. I also try to comment files when I remember.
I can usually remember about two hacks back, more than that and I'm stuffed.
Of course, upgrading a site (different version numbers)causes major headaches where hacked core files are replaced. I usually redesign my sites (new theme etc) when a new release comes out, though I skipped everything between 2.0.13 and 2.3.0 as I couldn't bring myself to do all those hacks again.
2.3 has made me rebuild completely, and it's probably a good thing too. Keeps my users interested.

I think admin notes page inside administration panel will be good idea. I saw it in vbulletin forum and joomla, admin notes allow administrator to write notes about todo, upgardes, modules problems, his modifications and hacks.

For now, try ToDoMod