Openboard whiteboard is extremely easy to use. Supported platforms are Windows (7+), macOS (10.9+) and Linux (tested on 16.04) . It’s a free and opensource online whiteboard which is best for teaching math classes online. It has math tools such as compass, protractors and ruler, and it can handle documents from within the openboard whiteboard application.
There are also other whiteboard such as Google Jamboard , Microsoft Whiteboard , OpenBoard , BitPaper , AWW , Ziteboard which works as well as Openboard . More Info about this : The 10 Best Free Digital Whiteboard Software for Online Teaching,virtual classroom and distance education/learning|XP-PEN