Download of IDBS XLfit5 5.3.1.3 was on the developer's website when we last checked. We cannot confirm if there is a free download of this software available. This program is an intellectual property of IDBS. We recommend checking the downloaded files with any free antivirus. The software belongs to Education Tools.
From the developer:
XLfit is a powerful curve-fitting and data analysis package that integrates completely with Microsoft® Excel. XLfit offers an extensive selection of data analysis and calculation tools, including a superior range of fit and statistics models as well as charts and graphs to visualize, interpret and present experimental data, all in Excel.
You may want to check out more software, such as IDBE Tools 2010, IDBE RibbonCreator 2013 or Database Window for Access 2010, which might be related to IDBS XLfit5.