Firefox is a popular browser from the Mozilla Foundation that is the descendent of Netscape Navigator. Available for my platforms including Linux and Windows and used by ~25% of all users. (Based on w3schools website statistics from Nov 2014 ⬀)
Chromium is the Open Source browsers that Google's Chrome is derived. Both are Blink/V8 based browsers but were previously Webkit based. Chrome is now estimated to be the most popular browser on desktops.