Scout!

An uncompromising mature enterprise-level platform designed for real-time monitoring of millions of metrics collected from tens of thousands of servers, virtual machines and network devices, effortlessly scaling to even larger environments.

Join millions of IT professionals and download Spiceworks, a free network monitoring software with network management tools, help desk ticketing app, network mapper and more.

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.

An advanced, easy-to-use monitoring solution for your entire network. The software's features include: up/downtime monitoring, traffic and usage monitoring, packet sniffing, failover clustering, in-depth analysis and concise reporting. A user-friendly web-based interface allows users to quickly auto-discover and configure the network devices and sensors they wish to monitor. All common methods for acquiring network usage data are supported: SNMP and WMI, Packet Sniffing and NetFlow / sFlow / jFlow. It also offers SMTP/IMAP Roundtrip-Email Monitoring and VMware Monitoring, VoIP Monitoring, Toplists for Packet Sniffing and Netflow Sensors, as well as sensor aggregation using its built-in Sensor Factory. PRTG Network Monitor includes more than 200 sensor types for all common network services (e.g. PING, HTTP, SMTP, POP3, FTP, SSH etc.), allowing users to monitor networks for availability, speed and failures. As soon as an outage occurs, alerts are sent via email, SMS, pager messages and other means. Request times and downtimes are recorded in an internal database, making it easy to compile performance, downtime and SLA reports. Monitoring, reporting and notifications can be automatically scheduled at specific times. High Availabiltiy is guaranteed by the innovative failover cluster, and remote probes can be used for easy multi-location monitoring. Network maps can be created which provide users with a unique visual network management tool. PRTG Network Monitor's Freeware Edition is completely free for personal and commercial use. The Commercial Editions are required if you want to monitor more than ten sensors. »

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.

OpenNMS is an enterprise grade network monitoring and network management platform developed under the free software or open source model. It consists of a community-supported, free-software project as well as an organization offering commercial services, training and support.

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.

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.

Dynatrace Ruxit provides all-in-one monitoring and operations management for DevOps teams working in startups, mid-sized companies, and large organizations. Using proprietary artificial intelligence technology, Ruxit enables companies to manage thousands of servers using a simple interface.

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.