I don't know any tools, but I'm sure they exist if you google them.
If it was me, without prior knowledge, I may export data to a flat file (.csv) and create either a stored procedure or an SSIS package to import the data into SQL.
Python may be my choice to automate the exports in chunks overnight where SQL can handle the importation and cleanup.
mongoexport --host yourhost --db yourdb --collection yourcollection --csv --out yourfile.csv --fields field1,field2,field3
Doing it this way allows you to define the structure before it hits the SSIS package.
Another way
Here is a good example of doing all collections. This was from another answer.
out = `mongo #{DB_HOST}/#{DB_NAME} --eval "printjson(db.getCollectionNames())"`
collections = out.scan(/\".+\"/).map { |s| s.gsub('"', '') }
collections.each do |collection|
system "mongoexport --db #{DB_NAME} --collection #{collection} --host '#{DB_HOST}' --out #{collection}_dump"
end