Linux applications are all mostly small and lack of expert systems(wizards). And it is written in file system(scripts) to use randomly assembled library of languages, scripts and utilities. Because all programming is done by file system, it is difficult to do bug fixing, unless you use text editor on such file system and you have to be fluid with languages, scripts and utilities in the file system.

Having said that, you still can link many file systems together in one mother of a killer application.

First, you need wordprocessor to make customers work for you and fill out the form for credit, insurance or payment methods. Then you need spreadsheet forms to get the scheduling done. Then you need supply chain software to deliver goods, or streamlined labor process(schedule form) to do service for the customer one step at a time.

Once you see the block diagram of such a killer application; you can find the Linux 30,000+ commandline software to cut and paste to a quick makeup of a killer application.

Good Luck, Linux is for applications, especially killer applications.