Web sites are all about giving people a way to interact with your business. From the prospective client looking for information to the staff member booking resources, web sites are more than static sales pamphlets.
Even though the internet has become so available, I would not open a web browser to run my home automation or format a USB stick.
Desktop software provides a way for the user to interact with the physical machine they are on, and is often the product in itself.
Mobile applications can provide an interface into your business much like a web site, but faster or convenient.
A mobile app may also be the product itself as a game or utility.
The development of an API is to formalise how other systems talk to yours. This can take the shape of a mobile app exchanging information with your database, or a client's software using your hardware. The core principals are stability and security.
Why Bespoke Software?