This module provides a new field type that allows you to select other fields from that content type (or any bundle), and it will concatenate their display values into a single field on save.
The example use case is then using the field as an exposed filter in a View.
Ideally you would use Apache Solr for this sort of thing, but in some cases when your theming focuses on view modes and formatters, and not Views output (by using Display Suite, for example), it allows you to build a regular view and still have an easy search across all fields.
The initial approach to this is using the Entity module, but improvements and suggestions are more than welcome.
Development sponsored by Stanford GSB.