Project Invoice
This invoicing application stores all your data on your local machine. None of the data is shared between different browsers or computers. You can however sync your data peer-to-peer (meaning from your computer directly to your mobile). It is a perfect example of local first software.
Project Invoice is accessible offline after the application has been loaded for the first time. You can turn it into a mobile-web-app by using the add-to-home-screen from your mobile browser.
You can use it to create quotations and invoices, and create quarterly and yearly summaries for bookkeeping. Using some CSS you can completely style the invoices to your liking.
