I believe what the author is describing is called A Desktop Application. They were these crazy forms of web apps, that ran on a local computer, stored data locally, and didn't use a server. Or a web browser. Legend has it that they used little memory, were fast and snappy, and enabled native integration with all of an operating system's capabilities, widgets, etc, while still allowing a user to completely control what happens with the data the program used.

Porting this type of application could take a lot of work! So at some point, somebody invented a programming language called Java, which used a thing called a Virtual Machine, so that one application could run the same way on any computer that could run the Java Virtual Machine. They called this A Portable Desktop Application.

Unfortunately, this obscure language was somewhat difficult to use, so this paradigm was abandoned for simpler languages, and with it, so went the idea of A Portable Desktop Application.

Decades later, somebody reinvented the idea. But it required a much more limited application platform, running inside a kind of hacked-together document viewer, with a simplistic programming language designed to control how documents were displayed. It took about 1000x as much memory and CPU, but, with addition of about 50 different frameworks and 30 different new custom APIs, you could finally get close to the same functionality as the first solution.

Ah, technological progress...