Oracle Live SQL
An easy way to try and learn new SQL and PL/SQL things
Access to hundreds of ready made scripts and more
Few weeks ago Oracle announced another great tool to help and make us developers more productive. It is a live PL/SQL environment in your browser without having to install anything.
You now have the ability (along with apex.oracle.com) to access online easily configurable environment to test, try your coding or browse community written examples to help you with your ideas.
Personally I think idea is brilliant, the more tools we have it makes our lives easier.
You can create your own tables, write and upload scripts, write your own queries plus be able to download and try many community written code.
If nothing check it out I am sure you will not be disappointed - Oracle Live SQL