After many years Packrat is no longer available for sale. The app has sold very little and 37signals stopped accepting new accounts for Backpack a few years ago (2011 I think). Even Everport outsells it, which is an app thats helps you move your Backpack data to Evernote.
As such, I no longer wish to support this app and it’s time to let it go. It was the first Mac app that I shipped and it was a lot of fun. I might bring the name back in another app that will not be connected to any 37signals’ service. If anyone is interested in purchasing the rights to Packrat, I am open to that. Just send me an email.