What is Redash?
So as Metabase, Redash is an Open Source data visualization software. The license of Redash is the BSD 2-Clause "Simplified" License which is slightly different than the one of Metabase GNU AFFERO GENERAL PUBLIC LICENSE.
The big difference in those two licenses is that the one of Redash, from my understanding, make it more suitable if you would like to make business with, as you can keep your modifications for you and make it as a paid software.
The other big differences between Redash and Metabase is that Redash allows the integration of data feeds such as csv and json which make it very interesting to use. But on the other hand Redash is quite difficult to install without Docker where Metabase can be install in just a second.