OpenKeyval.org is a completely open key-value data store, exposed as a drop-dead simple web service. The goal is to make this a very easy way to persist data in web applications.
curl -d "data=%00" api.openkeyval.org/testing
{"error":"missing_field","message":"Data must be sent as form data in the field 'data'","documentation_url":"http:\/\/openkeyval.org\/"}
curl -d "data=%00" api.openkeyval.org/testing {"error":"missing_field","message":"Data must be sent as form data in the field 'data'","documentation_url":"http:\/\/openkeyval.org\/"}