Current Sketch app version is 41 (page last updated November 8, 2016)
This page tracks the official direct download link to the most recent previous release (compared to current release). So, if you’ve upgraded to the latest version of Sketch and want to go back 1 version, you can find that link on this page.
Remember, you can have multiple copies of Sketch on your Mac. Simply put the version(s) in named Folders inside your Applications. Be careful to pay attention to which version is actually running, double clicking on a Sketch file will usually open the latest version that’s installed.
Download Previous Sketch app version 40.3
Full Sketch Version History (Official)
Sketch has completely revamped it’s product updates page! You can now very easily download any previous application version if desired.