nut is a project that has been around for decades, to allow monitoring of one or more UPS'.

nut began monitoring through a serial port, then when USB came along, added that. Now, it can handle network attached UPS' (snmp and ipmi), and many, many more.

nut is available for almost all operating systems (Windows appears a little buggy). nut comes in a client/server configuration, allowing one or more centralized monitoring servers to provide details about a server to other machines which may only have a client on them.

More information about nut can be found in the extensive documentation at:

https://networkupstools.org/index.html