An OTS file is a spreadsheet template created by the Calc program included in Apache OpenOffice (formerly OpenOffice.org) or another spreadsheet application that supports the OpenDocument standard. It contains a spreadsheet saved in OASIS' OpenDocument XML-based formatting. OTS files allow users to create multiple .ODS spreadsheet files using the same styles and formatting.

OTS file open in Apache OpenOffice Calc 4.1.3 Calc is one of several programs available in the OpenOffice suite. It is similar to the Excel program available in the Microsoft Office suite. The OTS templates are used to save spreadsheets that are repeatedly used such as invoices, budget planners, and calendars. In Calc, you can create your own templates with custom spreadsheet layout, data, fonts, and styles. You can also download templates from the OpenOffice website by selecting File → New → Templates and Documents and then clicking "Get more templates online...".