Let you define schemas for data fields, which you can assign to pages. When editing a page you can fill data according the schema. Data can be output as tables. Inline editing in tables. Updating a schema will update it for all pages.
The Struct Plugin is the new generation of Data plugin.
Let you use namespace templates which are editable by normal wiki users.
The default template pagenames are '_template.txt' and __template.txt, which are only editable as server admin. This plugin renames (in a configurable manner) these templates to normal wikipages.