You currently save your progress on the Numberslides platform and we keep a number of versions in our archive that you can revert back to. We are working on automatically backing up your data every few seconds. All your forecast and account information is saved securely in our online servers, ready for you and your invited users to access when you need it.
You can always download a copy of your plan as a PDF file to save to your computer, if you know you will be without Internet access for a while and want the content handy. But there's no need to save your data offline for backups.