If you're looking for a free and effective way to convert OLM files to PST format, there isn't a completely free standalone "OLM to PST Converter" tool available. However, you can use a manual method that involves some basic steps to achieve the conversion. Here's how:

1. Export Data from Mac Outlook:
   Open Outlook on your Mac and export the OLM file by going to File > Export. Save the exported file to your preferred location.
2. Set Up an IMAP Email Account:
   Use a free IMAP email service, like Gmail. Configure this account in both Mac Outlook and Windows Outlook.
3. Sync Data via IMAP:
   In Mac Outlook, move all your OLM file data (emails, contacts, etc.) to the IMAP account. Allow the data to sync with the server.
4. Access Data in Windows Outlook:
   Set up the same IMAP account in Windows Outlook. Once the synchronization is complete, your OLM data will appear in Windows Outlook.
5. Export to PST Format:
   Finally, in Windows Outlook, export the data to PST format by going to File > Open & Export > Import/Export, and choose the option to export to a PST file.

This method is completely free and doesn’t require third-party software. However, it can be time-consuming and may not work efficiently for large files. For faster and more reliable conversions, you may consider using a professional OLM to PST Converter tool that offers advanced features and automation.