Ask HN: How do you keep track of contracts and other documents?

A bit ago, one of my clients stopped answering my calls and emails. I went looking for the contract, to mention it, only to realize that it expired a couple months ago.

So, how do you keep track of all your contracts?

And how much interest would there be in an app for managing legal documents? Something that would send expiration alerts, keep track of revisions between you and your client, sign them digitally and have an "at a glance" view of all your documents with a client. I'm building a simple solution like this for myself, but if it'd help other people, even better.