Canister is a third-party Mac app that allows you to easily download your Basecamp files to your computer. It's priced at $9.99.
Whether you are looking to keep an archived backup or need a way to easily interact with your files, Canister can help. Utilize the power of Mac and Finder to easily interact with all your Basecamp files. With multiple-account support, you will be able to download all of your files, no matter how many accounts you work with.