I got a question from users while doing AMA on Twitter regarding the license of Vivaldi. I replied with a short answer due to Twitter’s character limitation but I thought I would post longer answer here.
Our source code package is available here: vivaldi.com/source. This links to a copy of the Chromium source code with the changes we made to allow our HTML/CSS/JS UI to run.
All our changes to Chromium source code are under a BSD license and hence can read by anyone. The details are explained in the the README and LICENSE files, within that package.
In addition, all of our UI code (included in normal packages) is written in plain, readable text. This means that all parts of Vivaldi are full audit-able and open from that perspective.