First think is to go find the key users (start from the CEO and work down) and find out what is important that it does to them. Map that. Find anyone technical

First think is to go find the key users (start from the CEO and work down) and find out what is important that it does to them. Map that. Find anyone technical who is still around and can talk sensibly about it and find out what they think is important. Map that. Use anything automated to map what it's up too (calling...) and find out where the core of it is. You may know what is important by this time, you will be able to make some sort of start...