Thanks to the update, both the Mac and iOS versions of iMovie, GarageBand and iWork apps - Pages, Numbers and Keynote - are now available to download for free from the App Store.
iWork documents on multiple Apple devices.
For reference, the entire iWork suite used to cost $30 on iOS and $60 on Mac, while iLife used to run for $10 on iOS and $20 on Mac. Previously, these apps were only "free" with a recent Apple hardware purchase.
It's not entirely clear why Apple chose to make these apps free to all applicable users, though it may have something to do with the growing number of free alternatives online. (Google has said that it plans to include new APIs and features focused on musicians in Android O.) Some are great, others are okay, but none of them are really bad, so they're definitely worth trying if you somehow haven't yet. Before today, those apps were free to users who bought a new Mac, iPhone, or iPad, and the free download was a one-time event.
iMovie, Numbers, Keynote, Pages, and GarageBand for both Mac and iOS devices have been updated and are now listed in the App Store for free. However, Apple has included its first-party apps for free with new iPads and Macs in the past, so you might already have already downloaded these apps.