Many times I was left scrambling to figure out, on what a particular DLL file does, its purpose or for god’s sake why does it even exist?. It will be good if we can have a central database of all DLL files (at least the popular ones).
And this is precisely what Microsoft’s DLL Help Database does. It is a database of all DLL files released with various products of Microsoft. Give it a search like ‘MSO9.DL’ and it comes back with this result page. Very useful, especially when you are debugging a fault or a bug.
As a related site, there is this 3rd Party site, which has a collection of hundreds of DLL files that you can download. Useful when a file is missing and you are not able to find the original source (CD). Since the site is not recognised by any of the leading software vendors, apply care before use.