nnir is a Gnus interface to a number of tools for
searching through mail and news repositories. Different backends
(like nnimap and nntp) work with
different tools (called engines in nnir
lingo), but all use the same basic search interface.
The nnimap and gmane search engines
should work with no configuration. Other engines require a local
index that needs to be created and maintained outside of
Gnus.