NIXStats!

Monitors your websites every 5 minutes, totally free. Get alerts by e-mail, SMS, Twitter or RSS. Add up to 50 websites. Monitors can be refreshed for an instant check with a click. Supports https and authentication with user/password.

Pingdom web site monitoring and other infrastructure for you and instantly let you know when anything goes wrong. Measure uptime, downtime, and the performance of your website as experienced by visitors.

Datadog is a monitoring service for IT, Dev & Ops teams who write and run applications at scale, and want to turn the massive amounts of data produced by their apps, tools and services into a unified view of IT infrastructure. Datadog's capabilities are provided on a SaaS-based data analytics platform that enables multiple teams to work collaboratively on infrastructure issues.

PHP Server Monitor is a script that checks whether your websites and servers are up and running. It comes with a web based user interface where you can manage your services and websites, and you can manage users for each server with a mobile number and email address.

Cabot is a free, open-source, self-hosted infrastructure monitoring platform that provides some of the best features of PagerDuty, Server Density, Pingdom and Nagios without their cost and complexity.

Track web page changes and get notified. Free Sign-up. Have all data in one place

PageMon.net: we're watching!

Comprehensive website and web application monitoring:* simulate a real browser (Firefox) to check performance* services monitoring (FTP(S), DNS, PING, TCP, SSL, SMTP, POP)* user experience monitoring (browser load time per user-agent, response time in various platforms* response time and throughput of each web transaction with graphical representation for quick performance insight* performance stats by ISP* application performance monitoring (monitor Java, .NET and Ruby on Rails web transactions and drill down to offending code and pinpoint root cause of issues from the cloud)* cloud monitoring (Amazon EC2, RDS instances and S3 Bucket)* VMware Monitoring* server Monitoring (Linux, Windows)* On-Premise Poller to monitor intranets* monitor from 3G/4G carriers* DNS server monitoring* SSL certificate expiration monitoring* notifications via SMS, Email, Push Notifications, Twitter and RSS Feeds* mail server, Exchange, FTP monitoring* API, user management* Root Cause Analysis - a comprehensive report based on trace route, ping output, DNS reports and web page screenshots that gives you a conclusion on what caused the issue »

Track web page changes in any web page daily for free users, every 30 mins for paid users - no RSS or Atom required. Receive notifications via Email, Notifo, Instant Message and SMS.

NodePing Server Monitoring and Web Site Monitoring. Simple but powerful Internet service monitoring. Checks as frequent as once a minute.

Port Monitor is an easy and online tool that does website and server monitoring for you 24/7 every 60 seconds and sends you or your co-workers instant email/push notifications when something goes wrong.

The AppBeat Android app lets you connect to your AppBeat uptime monitoring service from anywhere, anytime. You can view current live status of your checks and do basic check management:• Create simple web checks• pause/resume specific check or entire group of checks