Private Eye!

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. »

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Netactview is a graphical network connections viewer for Linux, similar in functionality with Netstat. It includes features like process information, host name retrieval, automatic refresh and sorting.