What Openverse is
Openverse is a search engine for openly licensed media run by the WordPress community. Its audio index gathers Creative Commons and public-domain sounds from Freesound, Wikimedia Commons and other collections.
Best for
Reaching Freesound and Wikimedia Commons audio without API keys, with the licence and credit line for each sound.
Licence and what it means for a release
Only Creative Commons and public-domain works are indexed. The licence of each sound is the one recorded by the original site; Sound Server reads it per sound and gives the same verdict as for the original source.
How Sound Server searches it
Through the public Openverse API, without a key. Openverse limits anonymous requests, so some searches return fewer results from it at busy times.