https://www.wikidata.org/wiki/Wikidata:Main_Page
Wikidata is a free knowledge database that has more than 90 million items.
You can query it using sparql (SQL-like) language. For example, a query to find rock bands that start with "M":
# P31 is for 'instance of'
# Q5741069 is for 'rock group'
SELECT DISTINCT ?band ?bandLabel
WHERE
{
?band wdt:P31 wd:Q5741069 .
?band rdfs:label ?bandLabel .
FILTER(STRSTARTS(?bandLabel, 'M')) .
}Another one to find the capital of France:
# Q6256 is for 'country'
# P36 is for 'capital'
SELECT DISTINCT ?country ?countryLabel ?capital WHERE {
?country wdt:P31 wd:Q6256 .
?country rdfs:label ?countryLabel .
?country wdt:P36 ?capital .
FILTER(STR(?countryLabel) = "France")
}