If you have any confusion to choose software to open an OST file without Outlook, so i can recommend that you can try eSoftTools OST to PST Converter Software because i across with same problem and it resolve my problem with losing any data of OST file.
It is safe and risk free from the harmful viruses for you system. It offers a free demo version for all users and convert 25 items of OST files with all mailbox items into PST, HTML, MBOX, EML, EMLX, Office365 etc. and other multiple files.
Read More:
https://www.esofttools.com/blog/how-to-open-ost-file-without-outlook/
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