FRT Freeware Tool is the best OST converter software for opening and converting Outlook OST files into over 8 different file formats, including PST, EML, MBOX, EMLX, MSG, and HTML. This professional tool is fully featured, allowing users to safely import OST into Gmail, Office 365, IMAP, and over 5 other email clients. Additionally, the software preserves the folder's original hierarchy during the conversion/migration process. The OST file converter has a user-friendly interface and is compatible with all Windows operating systems.