JupyterLab is a new web-based frontend that brings together many tools in an extensible, performant, open-source environment. We announced it to be ready for users about a month ago. We are calling it "beta" since the extension developer APIs for making extensions are still evolving.
This is JupyterLab. Create a new tab by clicking the + button or using the File | New menu. We can then start a notebook with a specific kernel, a console, terminal, or text editor.