Provides Oracle's database in-memory? I'm trying to find out, if Oracle's newest database release 12c comes per default as an in-memory database or does it use TimesTen for this feature?
According to Wikipedia (Oracle Database) it "utilizes TimesTen technology" for "In-Memory Database Cache".
Are those two different databases or is the one like a feature of the other?
The new Oracle 12c In-memory database feature is not the same as TimesTen. It implements a column-store based storage in memory in addition to the traditional row-based format on disk. So your data is held in BOTH formats simultaneously. You choose which tables you want to store in memory. This can allow immense improvement in mixed-workload databases.

It is an extra cost option, not included free even with Enterprise edition. The rationale is that if you are maintaining a separate datamart for your analytics, you could instead do the analytics in real-time right on your OLTP system with the In-memory feature and eliminate the need for a datamart environment and its cost (not to mention all the ETL work you have to do to maintain a datamart).

See: http://oracle-base.com/articles/12c/in-memory-column-store-12cr1.php

A short video on it: http://www.youtube.com/watch?v=8Yf1ghec0gU  

A longer video on it: http://www.youtube.com/watch?v=CjkPUg1m6PA