Yes, it is totally free to use and you can use it offline as well.
You can use it for both purposes. Also, you can customize it according to your requirements.
Right click on the launcher icon (next to chrome search bar), you will see a context menu. Select "Options", you will see all the options to customize.
By pressing Ctrl+S you can save it. It'll save with the .html extension but don't worry you can open it with chrome next time.
We don't save or upload your data to the cloud or any other server. Data only manipulate within the local environment. So you are 100% safe with TabNote.