json      - used by the encoding/json package, detailed at json.Marshal()
xml       - used by the encoding/xml package, detailed at xml.Marshal()
bson      - used by gobson, detailed at bson.Marshal()
protobuf  - used by github.com/golang/protobuf/proto, detailed in the package doc
yaml      - used by the gopkg.in/yaml.v2 package, detailed at yaml.Marshal()
db - used by the github.com/jmoiron/sqlx package
orm       - used by the github.com/astaxie/beego/orm package, detailed at Models – Beego ORM
gorm      - used by the github.com/jinzhu/gorm package, examples can be found in their doc: Models
datastore - used by appengine/datastore (Google App Engine platform, Datastore service), detailed at Properties
schema    - used by github.com/gorilla/schema to fill a struct with HTML form values, detailed in the package doc
asn       - used by the encoding/asn1 package, detailed at asn1.Marshal() and asn1.Unmarshal()