The Core Field Types module is included in all Form Tools download packages from 2.1.5 up to 3.0.0, where it has been incorporated into the core). It is used by the installation script to populate the database with the Core field types for use in your forms. Namely:
- Radio buttons
- Multi-select dropdowns
- Phone Numbers
- Code/Markup fields
This is a special module. Since it handles key functionality, it cannot be uninstalled.