http://opendata.government.bg/
http://www.smartdatacollective.com/bernardmarr/235366/big-data-20-free-big-data-sources-everyone-should-know
https://www.forbes.com/sites/bernardmarr/2016/02/12/big-data-35-brilliant-and-free-data-sources-for-2016/#315a174ab54d
https://www.creativebloq.com/features/best-javascript-apis