Packrat is the premier desktop client for 37signals' Backpack web application. Packrat lets you use your Backpack account when you're offline. Before you hit the road for the first time with Packrat, just use the Synchronize command to sync with Backpack and all the data from your account is duplicated on your Mac. View and edit your data offline or online. When you're online, Packrat will automatically inform Backpack of your changes and your account is kept up to date.