It is an online application in which you can select to work some of supported RDBMS.
There are 2 text area fields: first is used to set your schema and data, the second is used to write some query that will run against your schema and data.
Using SQL Fiddle you can share your script similar to Gist for source code sharing.
It is also useful as online SQL code beautifier and formatter.
Here is an example of SQL Code for Oracle DB: http://sqlfiddle.com/#!4/1897b/1