What is Blockstack browsers?

There is this thing browser.blockstack.org/ . What is that? Is it just a marketplace? In the docs you can find that you need to download the software on your computer to use Blockstack apss. But also, it says:

If you use our Web-hosted Blockstack Browser, you can get started using DApps right away.

So what is this browser? And do I need to install anything or I can use the web-hosted version?