1.Tableau Online: Is an online hosted Tableau Server, owned and run by Tableau themsleves. You pay them an annual subscription for the users who will connect to this service. But the cotent that is published to it is secure. Effectivily you are hiring a Tableau Site from Tableau. Great for those taking their first steps with Tableau.
2.Tableau Public: is an online service hosted by Tableau. There is no security, so anyone can access published content. Not good for business stuff, but a great resource learning from others via the online content
3.Tableau Reader: Is a free tool that is used to work with dashboards. Works in the same way has Tableau desktop, but you cant edit content. You can just interact with it. The content is in the form of a packaged workbook (a workbook that holds both the dashboards, and the data). There is no ability to connect Reader to Tableau Server, so the data in the packaged workbook is static. ie it is as-of the time the packaged workbook was created
4.Tableau Digital: Dont know what this is. Dont think that it is a product.
5.Tableau Mobile: is an app (for android and ios) that lets you connect to tableau server and online dashboards. It has been optimised for mobile devices to make interacting with dashboards easier.
Hope this helps
Tableau Reader is a good alternative when a report consumer cannot use Tableau Server. Instead of publishing your Desktop report to Server you instead save it as a packaged workbook, a .twbx. This packaged workbook can be emailed, copied to a network file share, etc. that others can open using Reader (which is FREE). They can filter and use parameters and all the necessary data for the report is contained, or "packaged", with the workbook. The workbook does not have the ability to connect to data sources so there's no need to worry about drivers and ODBC connections
We used Reader for outside customers who cannot access our Server and our field and sales people use Reader when they are on-site with an external customer or other location where there is no internet access.
Tableau Public is good for sharing vizes when you want it to be easily seen by the public. In particular, journalism and non-profits can benefit from this free "service"
It does have restrictions of course. You can learn more here: Tableau Public Frequently Asked Questions
Thank you all for the prompt response. It was helpful