GNU Recutils is a set of tools and libraries to access human-editable,
text-based databases called recfiles.  The data is stored as a sequence of
records, each record containing an arbitrary number of named fields.

Advanced capabilities usually found in other data storage systems are
supported: data types, data integrity (keys, mandatory fields, etc) as well
as the ability of records to refer to other records (sort of foreign keys).
Despite its simplicity, recfiles can be used to store medium-sized
databases.

Recfiles are human-readable, human-writable and still they are easy to parse
and to manipulate automatically.  Obviously they are not suitable for many
tasks (for example, it can be difficult to manage hierarchies in recfiles)
and performance is somewhat sacrificed in favor of readability, but they are
quite handy to store small to medium simple databases.

WWW: http://www.gnu.org/software/recutils/