You can use a stock rdbms and still keep track of changes. Just keep a seperate "Updates" table which consists of the tuple {class, object, change-description, changed-when, changed-by}

You don't need both class and object, but I prefer to log both object type and id.

Anything that touches financial records-keeping would be ripe for this kind of software, too. I spent quite some time on a financial services system and our number one enemy was mutable state.