Oracle database 19c
Oracle database 19c is currently available at LiveSQL.oracle.com and on premise Exadata. LiveSQL is a free online platform that can assist with development and training.
Other on premise releases are expected in the next few months of Q2CY19.
19c is the long term support release of 12cR2 with extended support until Mar 2026. Extended support is currently available for specific release patch sets (known as the terminal patch set) 220.127.116.11 (11gR2) until Dec 2020 and 18.104.22.168 (12cR1) until Jul 2021.
It is highly recommended that you upgrade your databases to 19c when available for your platform.
Oracle database 19c whitepaper
Read the whitepaper if you want to learn more about this release.