collectd is a daemon that periodically collects system and application performance metrics. It stores the values, for example in RRD files, or makes them available over the network to other tools. It ships with a large number of plugins, from common use cases to very specialised topics. It is written in C for performance and portability, so it can run on systems without a scripting language or cron daemon, such as embedded systems. It is distributed as source code and run by the user itself rather than offered as a hosted service.
collectd is free and open source software, developed in a public GitHub repository. The core daemon is licensed under the MIT licence, and each plugin carries its own licence, mostly MIT or GPL. Because collectd runs on infrastructure you control, no metrics leave your environment unless you configure a plugin to send them elsewhere. For a European organisation this means no dependency on a vendor-operated service or on a particular jurisdiction for the collection layer.