I think the EPC (energy performance certificate) dataset in the UK is a nice example of this. Anyone can download a full dataset of EPC data from https://epc.opendatacommunities.org/

Admittedly it hasn't been cleaned all that much - you still need to put a bit of effort into that (newer certificates tend to be better quality), but it's very low friction overall. I'd love to see them do this with more datasets