It allows you to move tabs into named groups. Only tabs from the active group are shown in the tab bar, and you can switch between groups using an icon in the toolbar.
I do love that tab groups are malleable to the user's concept of organization, not some artificial notion such as grouping by website.
The end of Panorama (or Tab Groups as known nowdays) was a disaster for me, as I don't hesitate having over 3k tabs open.
Works similar to tab groups, but each group is in it's own container.
When I open up a tab group with many tabs in it, the extension loads all of them up (snoozed) in a way that takes a little bit of time to complete, but it works well.