OpenTSDB - OpenTSDB is a distributed, scalable Time Series Database (TSDB) written on top of HBase.
Pingdom - With website monitoring from Pingdom you will be the first to know when your website is down. No installation required. 30-day free trial.
Axibase Time Series Database - ATSD is purpose-built for analyzing and reporting on massive volumes of time-series data collected...
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
RRDTool - High performance data logging and graphing system for time series data
Better Uptime - We call you when your website goes down