According to me, OST to PST Converter Application is the best tool to convert OST files into PST, EMLX, EML, MBOX, MSG, HTML, HTML, and ICS formats as it comes with latest features as specified below.

Unique & advanced solution to convert data from OST to PST Outlook- updated features-

Fix all types of Outlook errors, corruption and etc.

migration of mailbox items such as Emails, folders, contacts, properties, attachments and etc. of .ost files into Outlook PST

Restore deleted items of .ost file into outlook.

Convert ost to pst outlook and 14 plus file format.

Free option to split large PST files.

No requirement of MS Outlook.