What are the most productive ways to spend time on the Internet?

1. Wikipedia : Most people get to Wikipedia through the search. However, their main page contains curated collections on topics that  you would have no idea of. Good ways to open your mind to new things.
2. Grovo: Build your Internet skills 60 seconds at a time. 
3. Lumosity: Brain Training. Like any other muscle, our brain needs a constant workout. Lumosity provides a collection of exercises that sharpens the brain. 
4. Lifehacker: Find out ways to do everyday things better. Although, their quality has come down a bit, there are still plenty of gems hidden in there that could simplify things. 
5. Stack Overflow: If you are a developer, this is your library, town hall and temple. 
6. Gibbon - Playlists for Learning: Learn stuff from curated content. 
7. Learn X in Y minutes: Learn programming languages. 
8. Redhoop: Search through top online courses in Khanacademy, Coursera, Udacity and others.