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 2.5.5 locked up (not responsive) in OS X 10.6
Thanks for the info. I'm not aware of any incompatibility with Snow Leopard, though occasionally Simon can become unresponsive if it uses up all the available resources. Have a look in the Console log to see if any errors were logged at that time.
You can reduce the chance of that happening by ensuring the tests are adequately spaced out, so there aren't lots running at the same time. I have some ideas to eliminate this risk in a future version.