Prevayler is a great persistence engine for Java. I've used it a couple of times at home when I needed to persist small amounts of data. Prevayler is based on Serialization and the Command pattern. Overall the engine is pretty fast and lightweight. Writing code to use Prevayler is fairly simple. You just have to put your collection into Prevayler and create command objects for every update. The collection and commands have to be serializable.
So now that I'm working in the .Net world, I had a need to persist a small set of objects. I found Bamboo.Prevalence on SourceForge. I was real excited to find a prevayler for .Net. So I started a test project to get familiar with Bamboo (v184.108.40.206). My simple test failed. I kept getting mysterious exceptions while creating the Bamboo engine. So I thought I would look for docs, but there were none. So I thought I'd look at user groups / mail-lists; they were practically empty. I found a couple of articles, but they were out of date. Bamboo's API has changed since the articles were written. So Bamboo is now getting deleted from my disk. It is a tragic end. Using undocumented open-source is not practical.
Recommended: Prevayler for Java
Not Recommended: Bamboo.Prevalence v220.127.116.11 for .Net