As part of their YesSQL campaign, Oracle has been promising an online tutorial site for playing around with SQL - and now it's here! You can go to https://livesql.oracle.com now to play around with creating objects, running SQL statements and even follow tutorials.
All you need is an Oracle.com account and (true to Oracle form) scroll through a very long page of legalese saying you can't keep any important data here. But after that, you're free to play.
The site offers quite good script management, where you can create and save scripts. You can even share them or run community-supplied scripts.
The user interface probably as good as a browser based SQL interface can be, and Oracle is offering some interesting shortcuts like the ability to create database objects in an abbreviated syntax. In this way, you can just list your column names and they'll all default to VARCHAR2(4000) unless you specify otherwise (e.g. by just writing n to indicate a number).
Check it out!
Thank you Sten for this useful information!