[hennell]

The linked product page seems to sum it up pretty well:

>We built Fleet to be a fast and lightweight text editor for when you need to quickly browse and edit your code. It starts up in an instant so you can begin working immediately, and it can easily transform into an IDE, with the IntelliJ code-processing engine running separately from the editor itself.

It's splitting the difference between text editor and IDE. It's their answer to people complaining "IntelliJ takes too long to start up" while keeping the IDE features that you lose just using a text editor.