The best alternatives to Snitch are Flywheel, haveibeenexpired, and Octopus mini. If these 3 options don't work for you, we've listed a few more alternatives below.
Flywheel is managed WordPress hosting built for designers and creative agencies. Build, scale, and manage hundreds of WordPress sites with ease on Flywheel.
Monitor your SSL certificates on *every* host in your domains for free. Get notifications prior to certificate expirations, and never experience an outage again.
Nodeify allows you to keep track of and monitor any website's SSL certificate. When you register and add a domain into monitoring the app will alert you, based on the notifications you setup, of any updates, issues, and/or upcoming expirations.