Replicating data from Oracle to MySQL
From your question, it doesn't sound like you need true transactional semantics, and that asynchronous replication would be fine. 

If that's the case, it's fairly trivial to build a replication system using triggers within Oracle to track data changes, and then replaying those changes into MySQL, using something like perl (or other scripting languages) as the glue code to talk between both systems using SQL. 

This might sound like it would be a lot of overhead, but we've built numerous systems like this for our clients, and the overhead from Oracle's standpoint is pretty low; we've run it on some OLTP systems powering top 1000 websites that had hefty transactional workloads, and Oracle handled it like a champ.