The open-source "MySQL" database is extremely popular. It powers the site you're reading now. Until recently, however, not that many CMS vendors supported it. Of course, MySQL has its limitations: it's not transactional and isn't optimized for rapid updating. However, it supports very fast "reads," which makes it great for publishing high-traffic dynamic sites where there aren't a lot of content contributors to compete for server resources. FatWire just announced support for MySQL in its lower-end "Spark" product which serves as a CMS back-end to various Java Portal products (like Sun ONE). Nonetheless, MySQL support presents an architectural dilemma for other CMS vendors who rely on native tools within commercial RDBMSs to conduct basic repository services like roll-back -- tools that don't exist (yet, if ever) in MySQL...
Read More About Spark