Calculated spreadsheet-like fields?

Is there a module that will let me take the contents of a field containing a value, and calculate a new value that will be placed in another field.

For example, a field contains a numeric value, and I want a new value, "field value x 15%", is stored in a new field.

Ideally, I'd like to be able to define all kind of field value calculations, maths, and string manipulations.