Do you want to open OST file without Outlook, but you didn't get the best solution I suggest you get eSoftTools OST to PST converter software. This tool has a 10+ file format for conversion such as OST to PST, EML, EMLX, office 365, HTML, Yahoo Mail, Gmail, etc. It has a demo version that can allow users to convert 25 items from each folder. It supports all Windows OS. This software recovers all deleted emails and converts them into PST.