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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.

Monitors the performance of your websites, DNS, and email servers along with blacklist monitoring. Get alerts by e-mail and SMS. Add 1 monitor for free. Plus free online network and DNS lookup tools.

Mist.io is an open source software and a freemium service that helps you manage and monitor virtual machines (VMs) across multiple public, private and hybrid clouds using your mobile phone, tablet or laptop.

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 »

Hosted status pages with a focus on automation of monitoring and notifications, for keeping your audience informed of uptime issues.

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

Monitis is a Cloud monitoring and IT analytics service offering Website Monitoring, Server Monitoring, Network Monitoring, Application Monitoring, Cloud Monitoring, and Custom Monitoring.

Free open-source website monitoring software, easy to set up and use for monitoring web sites. You can monitor single web pages, multiple web pages, pages in sitemap and even your whole web site using spider. You can check HTTP result codes and even contents of the checked pages. Website checking is done periodically using build-in cron mechanism. In case of a check failure, application will automatically send email to site administrator.

Uptime monitor for server. Currently fully free (beta) so it is subjected to change. Allows to monitor unlimited servers and websites. With custom CNAME you can create live status pages.

"Is It Down Right Now" monitors the status of your favorite web sites and checks whether they are down or not. Check a website status easily by using the below test tool. Just enter the url and a fresh site status test will be perfomed on the domain name in real time using our online website checker tool.

RapidSpike is an uptime and performance monitoring service for websites and web applications. It simplifies monitoring, alerting and reporting to support your online presence and to ensure a positive user experience. Organisations use it to identify problems, measure performance and improve capacity planning.