Database
[{_id:1,name:"Dennis",tasks:[{task:"Drawing",dateFinished:ISODate("2013-06-07T00:00:00Z")},{task:"Paint",dateFinished:ISODate("2013-07-07T00:00:00Z")}]}]
Query
db.collection.aggregate([{"$unwind":"$tasks"},{"$sort":{"tasks.dateFinished":-1}},{"$project":{"task":"$tasks.task","dateFinished":"$tasks.dateFinished"}},{"$project":{"tasks":0}}])