If you received a Notice to File a Business Property Statement from the Assessor and your business is no longer in operation, you are still required to file the Business Property Statement. You should also include a note on the Business Property Statement indicating that the business has closed, so the Assessor does not continue to assess the property.
New applications are launched on a daily basis and if you believe you have the skills to create your own and a unique enough idea, you should do it! Aside from the fact that you will have to invest little to no money to get started, it is far less time consuming than the average 9 to 5. Once you have created your application, couple it with the right marketing strategy and you'll be making money in your sleep. The best part about developing applications is that you can do it from anywhere in the world.