Database
[{"_id":ObjectId("54abcdbeba070410146d6073"),"name":"Product 1","isFree":true},{"_id":ObjectId("54afe32fec4444481b985711"),"name":"Product 2","isFree":false},{"_id":ObjectId("54b66de68dde7a0c19be987b"),"name":"Product 3","isFree":false},{"_id":ObjectId("54b66de68dde7a0c19bc897d"),"name":"Product 4","isFree":false}]
Query
db.collection.aggregate([{"$group":{_id:null,free:{$sum:{$cond:["$isFree",1,0]}},nonFree:{$sum:{$cond:["$isFree",0,1]}}}},{$project:{_id:0}}])