Oracle Database Standard Edition One is designed for deployment in small businesses, line-of-business departments, and distributed branch environments. It is available on single server systems supporting up to a maximum of 2 CPUs and is easy to install, configure, complete with built in self-management capabilities. Oracle Database Standard Edition One manages all your data, and allows all your business applications to take advantage of the proven performance, availability, security and reliability provided by Oracle Database, at a low entry cost. Oracle Database Standard Edition One provides complete upward compatibility with other Editions, protecting your investment as your usage requirements grow. Standard Edition One is part of the complete Oracle Database family, offering full compatibility and scalability to tackle your biggest challenges.
Enterprise Edition – Industry-leading performance, scalability, and reliability for OLTP, decision support, and content management
Standard Edition – Up to 4 processor version of Oracle Database 10g with Oracle Real Application Clusters
Standard Edition One – Up to 2 processor version of Standard Edition at an attractive entry-level price
Personal Edition – Full-featured version for individuals, compatible with the entire Oracle Database family
Lite Edition – Complete infrastructure to build, deploy, and manage mobile database applications
This information is from the Oracle site.