DeferPanic is described as 'Go application monitoring. Production performance graphs, alerts, error report collection'. There are more than 25 alternatives to DeferPanic, not only websites but also apps for a variety of platforms, including Linux, Windows, Mac and Android. The best alternative is Zabbix, which is both free and Open Source. Other great sites and apps similar to DeferPanic are Nagios (Freemium, Open Source), Sentry (Freemium, Open Source), Datadog (Paid) and Icinga (Freemium, Open Source).
Doctor Dump is a free crash reporting and memory dump analyzing service. Its work is to collect software problem reports (crashes, failures, assert violations and so on) from your customers all over the world, to group them and to give you all necessary data to fix the problem.
LANState is a simple NMS with the network topology mapping and device monitoring functions. Add hosts to a graphical network map and monitor their state in the real time. Receive failure notifications when hosts and services go down.
Hosted Graphite is a monitoring service for development teams who run applications at scale. We take the data produced by your apps and servers, visualize it on graphs, then let you act upon the data provided by beautiful Grafana dashboards.
Errbit is a tool for collecting and managing errors from other applications. It is Airbrake (formerly known as Hoptoad) API compliant, so if you are already using Airbrake, you can just point the airbrake gem to your Errbit server.