Solar Writer is able to create, edit and save various kinds of astrological charts and then display many different types of reports for these charts.
The program that creates the charts and displays the reports is different to the reports themselves - the program is the Solar Writer "engine" and the reports are contained in separate files to be used by the engine. Thus there is no point having the engine unless you also have one or more reports that the engine can use. Generally you need to purchase reports for the engine to use – however, if you are technically minded, it is possible to use the engine itself to create any reports you wish to use. Together, the program and the reports you have for it to use, make up the "Solar Writer system".
You will be given the Solar Writer engine with the first report you purchase. It is not possible to obtain just the Solar Writer engine on its own, you must purchase at least one report and you will be automatically given the Solar Writer engine with it. You then install both the engine and the report(s) you have purchased. Once you have the Solar Writer engine you don't need to get it again, until an updated version of it becomes available. What you can keep acquiring and accumulating is more reports, either purchased – or ones you have specifically created by using the Solar Writer engine to do so.