structured data is data that is composed of smaller well-defined and indexable parts.
Structured data may be textually represented via some data format, and perhaps stored in a DBMS. Data structures may be serialized into structured data for purposes of communication or persistence.
In one sense, any program or script ever written is a system for working with structured data, but there are also programs dedicated to structuring, querying, and archiving data. This is a list of such systems in the Tcl world. It omits more general dbms%database management systems, and focuses on systems that provide a more customized interface for managing data. Also excluded are systems dedicated to Vector or matrix algebra in Tcl and Numerical Analysis in Tcl, which are enumerated on those pages.