Open source ETL

I was visiting with someone the other day who mentioned they might eventually be moving to an area that, because of a variety of factors, is predominantly inexpensive and free software solutions. This person is very knowledgable about databases, ETL, etc. and would probably like to continue their work in this regard. I’ve seen some mention of this before. While poking around the other day, I ran across an open source package for ETL. While it’s simple, and somewhat limited it could serve as a starting point or a very inexpensive alternative for a small MySQL based mart.