WebGazer - Monitor your website's availability with WebGazer, review its performance and get instant notifications when your website goes down. No installation required and free plan available.
Polymail - Native email app for email productivity.
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Airmail - Airmail is a lightweight and lightning fast mail client for Mac.
Really Good Texts - Peruse ridiculously good text marketing
Morning Mail - A new way to manage your mail. Tinder for email.