Opera mini is a well known software, its a browser and available for both smartphones and feature phones as well.
I have been using it for 4 years and its still serves my purpose of fast browsing. It has data saving technology and it works really good, sometimes it saves 80% of my data which is great.
However it is meant for light using and downloading heavy files like greater than 100mb is not possible so developers should eliminate this problem.
But for browsing tasks like facebook and other casual songs downloading its great.