Packrat. Take your Backpack offline.  Packrat

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.

the killer syncing and offline Backpack client that does even more than Backpack itself
- David Chartier, The Unofficial Apple Weblog
If you’re increasingly getting frustrated with offline time, it might just be the solution you’ve been looking for.
- Giles Turnbul, MacDevCenter

Screenshots and Videos

Document Window screenshot Tags Browser screenshot Reminders page screenshot
Document Window Tags Browser Reminders page

getting started movie thumbnail auto upload movie thumbnail Editing a page movie thumbnail
Getting Started Auto Upload Editing a Page

Features

View and edit your 37signals' Backpack data offline and keep it in sync with your local copy. Work with multiple Backpack accounts.
Inline editing of page contents and reminders. Drag and drop to reorder page contents.
Toggle between showing all completed list items and truncating them. Delete all completed items in a list with a single click.
Image and attachments are downloaded during synchronization for offline access. Uses Growl to present your reminders even when Packrat isn't the current application.
Use Packrat in your Automator workflows with the Synchronize with Backpack Automator action Use AppleScript to manipulate your data in ways only you can imagine.