Simon 5 is coming soon!
Simon version 5 is currently in beta testing. It is a massive update, introducing a much-requested feature: syncing the Simon data between multiple Macs, plus a Simon Status service, a Link Checker filter, improved Find filter, iMessage and Speak Error notifiers, a new app icon, and much more.
Important: please note that Simon 5 requires a minimum of macOS 10.12 (Sierra), and will be a paid upgrade from Simon 4 after the beta. Purchasers since September 1, 2020 automatically get a version 5 license (that also works in previous versions).
Re: Simon 3.4 Download Damaged
That is a known issue with Simon 3.4. It dates from before the Gatekeeper (aka Developer ID) feature was introduced in OS X 10.6. You should only use this version on OS X 10.5; if you're on 10.6 or later, use Simon 3.6.1 (or the latest version) instead.
If you do need to run Simon 3.4, you can bypass this error by temporarily changing your Security & Privacy system preferences to allow apps downloaded from Anywhere. Once you launch it once, you can change this preference back to the previous selection.