Let me paint a picture as it's come into focus for me recently. Apple develops a protocol called mDNS for zeroconf via multicast DNS. They call it Bonjour and are serious enough about making it a standard they release a free software library called mDNSResponder to support it which runs on GNU/Linux, OSX, and Windows.
A community project, Avahi, implements their own mDNS suite for GNU/Linux. Avahi adds some nice features, such as dbus support. To help apps use either option they support compatibility with mDNSResponder's API.
It's great to have this sort of cooperative-competition, but they took this a bit too far by printing a nag warning when their mDNSResponder compatibility API is used by an application and otherwise pressuring mDNS-using apps to drop support for mDNSResponder.
I sincerely hope Python projects aiming to implement mDNS build against the mDNSResponder API, for cross platform support if nothing else, and encourage their users to avoid using Avahi when questions about this nag page come up.