Features:

* URI-based .xls templates
* Multiple worksheets per workbook
* Multiple datasets per worksheet
* Configurable starting coordinates for data sets
* Custom mask options for numeric/date types
* Cell formats (fonts, backgrounds, borders etc)
* Cascading template support for cell formats
* Many workbook settings (JExcelAPI)
* Many worksheet settings (JExcelAPI)
* Cascading template support for worksheet settings
* Headers/Footers, print areas etc.
* Comments
* Formulas
* URI-based images
* Hyperlinks

Planned:

* Multiple data cells per column
* Workaround for the 65k-rows limit of Excel
* Validations

Possible?
* Charts
* Property sets