I'm a researcher at the Music Technology group who works on freesound (https://www.upf.edu/web/mtg)
We also maintain Freesound labs, which lists a lot of projects and research made using content from freesound: https://labs.freesound.org/
FSD50k is our hand-curated dataset of sounds designed for research in sound and event recognition tasks https://zenodo.org/record/4060432#.X3xrgi8RqL4, http://dcase.community/challenge2019/task-audio-tagging