Thunderbird When we talk about open source software, we are talking about software that is free to download and its source code repository is made available and public to its users. Open source code can be modified and distributed with the users’ rights if they want to. Thunderbird is an example of open source developed by the Mozilla foundation. All known web browsers like Chromium and Safari are open source apart from Internet Explorer. Internet Explorer has remained closed source for a long time now.
