
If you own an older release, you can buy the newest software release at a special upgrade price. So if you purchase 9.0 that means you get 9.1, 9.2, and any other updates free. Any updates released for your initial purchased version are free.
Your software key will unlock both Camtasia on Windows and Camtasia on Mac (Camtasia is one product, with two platforms). The same goes for maintenance releases, so if it changes from 9.1.0 to 9.1.1, that’s free, too, until your next upgrade. If you currently have Camtasia 9.0 and it updates to 9.1, that’s a free change.
There are also free updates that come with each new upgrade.
If you have a maintenance agreement, the upgrade is free. If you choose to upgrade your current version of Camtasia to the newest installment, for example 8.0 to 9.0, you have to pay for that upgrade.