While searching for an alternative to the limit of 2 gigabytes of Microsoft Access, I found SQLite (http://www.sqlite.org/) a small software library (350KB) in C without external dependencies that implements a SQL database engine.
The source code for SQLite is in the public domain and supports multi platform databases up to 2 terabytes.
The simplicity of SQLite is comes from acting directly on a single file (a database) on the hard disk, not requiring installation, configuration or administration. Performing a backup boils down to copy the file to another location.
Another added advantage is its direct connection to the R (http://www.r-project.org) using the RSQLite library.