ORM (Object Relational Mapping) Tools

I was an early advocate and user of O-R tools since 2004. When first introduced to Expresso. Now popularized through Hibernate, I have used first Expresso and then Keel's version of same, and also spent a few months using another tool called [can't remember] during 2003-2004.
The syntactical and or semantic differences between the various tools are not great, and I would feel comfortable tackling any such usage as required by a contract or job.