Ask HN: Has anyone sold a "fork" version of their web app?

So my app made it onto Lifehacker over the weekend. (http://lifehacker.com/5874115/ikeepm-is-a-simple-free-inventory-for-all-your-stuff). Since then, I've gotten over 1700+ signups, granted a lot of it are just folks who are curious but nonetheless, I do have a lot of folks who are using it.

A couple of days later I received an email from a marketing manager of a company. She expressed interest in buying a "fork" version of my app. Needless to say, I'm speechless and things are happening so fast. What turned out as a side project that I had hope to monetize one day, is now in consideration to be bought by a real company.

Has anyone experience this? She's asking for a price and I'm stumped. It's definitely a good problem to have, but I need to be careful.