Often refered to by the version numbers, e.g. “Oracle 11g” or “Oracle 12g”.
Meaning of the letters I could find:
Apparently those map to different architectures, whatever that means considering it’s closed source.
Default port: 1521 in older versions, 2843, 2844 in more recent ones.
11g has a free version called Express Version (“EX”): http://www.oracle.com/technetwork/database/database-technologies/express-edition/overview/index.html with max 10GB storage, 1GB RAM and 1 core.