Port Monitor!

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.

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.

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 »

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

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

Opsview Atom is ideal for personal use, SoHo setups, test or lab environments or just to get your hands dirty with all of Opsview's monitoring functionality!

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

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.

PushMon is a new kind of cloud-based monitoring system. Instead of checking public facing servers on a regular basis, PushMon will wait for pings from the objects being monitored. These objects are usually batch jobs, scheduled/cron scripts, backups, or test scripts, but really are anything that has access to the internet and can call a URL on a regular basis. If PushMon does not receive the URL "ping" by the specified schedule (like every hour, or every day or even by 5:00 PM every Fri), it will send an alert (email, IM, SMS, Twitter and/or phone call). We can monitor your database backups, your cron scripts, your background tests, your internet connectivity, your batch jobs, and a lot more. We also have an advanced but easy to use scheduling feature to alert you of problems as soon as possible. »