Over time, the spreadsheet grew into what we see today, in the form of Microsoft Excel and a number of similar products on the market. The power of the spreadsheet has grown almost exponentially, allowing the user to create customised formulae, charts, pivots and so on. Worksheets can be linked and updated automatically.
You can also create a calendar with a spreadsheet application and keep it within your budgeting workbook. You can list dates bills are due and you can also use the calendar in accordance with your budget to plan for special items or vacations. Having everything in one place will make it easier to manage your finances and plan for the future.
You'll need to include more than a basic level of development and calculation in your spreadsheet. There are lots of free spreadsheets on the web. Most of which are very simple and easy to build. People aren't going to buy a spreadsheet that they can get for free. Take yours to the next level by adding all the value you can imagine. Then research on how you can offer a little bit more on the development and functionality side.
One user at a time : In the instance where there are a number of people required to work on a spreadsheet, they can only access it when no-one else is working on it.