By and large this is a quiet update, with most of the work being done under the hood. Some noteworthy changes:

• Some built-in effects are realtime capable now
• A new Shelf Filter effect has been added, it’s in the EQ & Filters category
• An initial (beta) version of a beats and measures feature has been added, you can enable it via View → Toolbars → Time Signature Toolbar (beta), then right-clicking the timeline to change to beats and measures, and then changing the snapping and time and selection toolbar clocks to a beats format.
• A new vertical ruler (Linear (dB)) has been added, you can enable it by right-clicking on the vertical ruler.
• Project Rate has been moved to the Audio Setup button → Audio Settings and renamed Project Sample Rate

More changes can be found in the changelog: Audacity 3.3 – Audacity Support

You can download Audacity 3.3 from audacityteam.org/download.