Monitority - Simple website monitoring service (sms/email alerts)
SE Ranking - All-in-One cloud-based SEO software for agencies, marketing teams and webmasters
Suprvise - Know instantly when your sites are down.
DeskAlerts - Send alerts to any corporate device: PCs, phones, tablets, etc.
PingPing - A simple tool to monitor your website and SSL
SEMRush - All-in-one Marketing Toolkit for digital marketing professionals.