self-hosted
Information about nice self-hosted apps we find usefull.
DNS
Pi-hole - A blackhole for Internet advertisements with a GUI for management and monitoring. (Source Code) EUPL-1.2 Shell/PHP
TeemIP - TeemIP is an open source, web based DDI (DHCP, DNS, and IP Address Management (IPAM)) tool. (Source code), (More info).
IT OP management
iTop - iTop stands for IT Operational Portal. iTop is an Open Source web application for the day to day operations of an IT environment. iTop was designed with the ITIL best practices in mind but does not dictate any specific process, the application is flexible enough to adapt to your processes whether you want rather informal and pragmatic processes or a strict ITIL aligned behavior.
At the heart of iTop is the CMDB (Configuration Management Data Base), this is originally the first part of iTop that was developed. Then came the tickets and all the derived processes. (More info)
Monitoring
Nagios core - possible to run on Raspberry Pi (from source code).
Icinga2 - fork of Nagios. Can be installed to Raspberry Pi from package