Several vendors do provide solutions to synchronize data between databases from different vendors. For architects known to the Oracle portfolio a known solution is making use of Oracle Goldengate. Less known are the solutions from Attunity. A solution for syncronizing data from a source to a target database which do not have to be from the same vendor is provided in the form Attunity Replicate. One of the big advantages from Attunity Replicate is that it is not needed to have a direct SQL connect between the source and the target system, this can be extreme valuable in cases where you might experience a lot of latency and the replication will not have to be (near) real-time.
In the below video is a short demo given on how to setup a replication of data between a Microsoft SQL server and an Oracle database by making use of Attunity Replicate.