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.
Nova Inbox - Personalize emails in seconds, right from your inbox
Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting
Gmail Mail Merge - Send personalized emails with attachments
NIXStats - SaaS monitoring tool for window/linux servers and websites. Think up-time robot but with more features.
InboxSDK - First usable API to write Gmail Apps for 1B active users