A Web Whiteboard
This is a very good interactive whiteboard that is online.
Twiddla
This is a very good and simple online whiteboard.
Apps
Explain Everything EDU Honorable Mention
This is one of the most popular whiteboard apps around. You can record a lesson with this app. You can even make slides similar to a PowerPoint.
https://apps.apple.com/us/app/explain-edu/id431493086
Windows: https://www.microsoft.com/en-us/store/apps/explain-everything-interactive-whiteboard/9nblggh5gcw8
Google Play: https://play.google.com/store/apps/details?id=com.explaineverything.explaineverything
Chrome: https://chrome.google.com/webstore/detail/explain-everything-whiteb/abgfnbfplmdnhfnonljpllnfcobfebag
Explain Everything Interactive Whiteboard
https://itunes.apple.com/us/app/explain-everything-interactive-whiteboard/id1020339980?mt=8
Website: http://www.explaineverything.com/
https://whiteboard.explaineverything.com/
Educreations
This is one of the most popular free whiteboard apps. The app has a simple user interface and is a good whiteboard app. You can record lessons then share the lessons with students via the web. If you see the videos that teachers have created on the Educreations website, you will have better ideas of how why this app is popular.
https://itunes.apple.com/us/app/educreations-interactive-whiteboard/id478617061?mt=8
Vittle
This is an app that allows you to annotate your pictures and PDFs. You can add audio and turn your presentations into cool videos.
https://itunes.apple.com/us/app/vittle/id629037418?mt=8
Website: http://www.qrayon.com/home/vittle/
LiveBoard Interactive Whiteboard
This is a whiteboard app that helps people collaborate on a task.
https://play.google.com/store/apps/details?id=com.inconceptlabs.liveboard
Whiteboard
This is a simple but effective whiteboard app.
https://play.google.com/store/apps/details?id=com.vistrav.whiteboard&hl=en
Software
OpenBoard
This is free whiteboard software for Windows or Mac computers.
http://openboard.ch/download.en.html