Keeping track of projects

Keeping track of projects

In my job I deal with several projects at the same time (and who
doesn't?). Sometimes I have to make changes to a project which I dealt
with half a year ago or even longer. And it's hard to recollect the
details about the project. I usually look for the modification dates of
the files, then I start digging into my email to find the relevant
conversations. If the project is really small then it's not even in
company's VCS. Sometimes it takes much longer to recollect the details of
the project than to make the required change. I started using Onenote to
keep track of relevant information about projects but I didn't succeed
much in this, probably because I don't have a clear picture of how this
knowledge base should look like.
It would be nice if I can use some automated tool which can connect
relevant emails, source codes, bugs information and feature requests and
time periods of different activities related to a particular project. With
advanced search capabilities.
How do you keep track of this information?