You can download Oracle 12c R2 database now. Only Linux x64 and Solaris Operation Systems supported for now.
You can download with below link;
http://www.oracle.com/technetwork/database/enterprise-edition/downloads/index.html
Also you can find new features about of Oracle 12c R2 with below links;
https://docs.oracle.com/database/122/
https://blogs.oracle.com/sql/entry/12_things_developers_will_love