GroundWork Monitor Community Edition can give you insight into your computing infrastructure, allowing you to see the current and historical states of all your computers: servers, desktops, and laptops, all of your network devices, all of your services (like TCP/IP and Web services), and all of your applications (like mail servers and database apps). You can choose to be alerted when something goes awry via pager, SMS, email, or phone, and even set up automatic restarts or fall-overs.
GoAccess is a real-time Web log analyzer and interactive viewer for almost every Web server. It runs in a terminal and provides fast and valuable HTTP statistics for system administrators that require log monitoring and visual reports on the fly. GoAccess can monitor unique visitors, browsers, spiders, OS, hosts and IP geolocation, keyphrases, referring sites, status codes, etc. It has support for IPv6 and it parses nearly any Web log format.
LibreNMS is an autodiscovering PHP/MySQL-based network monitoring system forked from Observium. It aims to be easy to use and painless to deploy, and to support monitoring of a wide range of devices. Observium's license changed to a modified QPL license in May 2012, then was split into free and commercial versions. The aim of LibreNMS is to continue to create a usable NMS, but with a community focus and GPL licensing.