I like the ability of eclipse and other ides to open several projects at the same time.
On PHPStorm, that could be easy to implement by:
- Showing multiple "roots' on project sidebar, one for each project (each would be loaded on their own "class/index" space completly independently).
- Tint the project file / folder structure with a 'pastel' color and use the same pastel color in the tabs of currently open files
- highlight the project of the currently focused file
Closer integration, harder to implement
- Add a quick and easy key combination / button on toolbar to call to focus the next project that is open
Very easy to implement, more loose integration
Both would facilitate the change of focus when one has several projects open at the same time.