You can't have multiple projects or windows open at the same time but with the "Open 2nd Session" feature you can open a second fw session which is a second second window of the WIFE Client application using the same User.
This will allow you to e.g. work on an Invoice but when needed to create or check a Booking this can now be easily done in the second session without the need to close all other windows first to go back to the Hourline and check the schedule, Project, Contact or else.
You can also open a project in each session and thus compare the both of them if you want.
To close the 2nd Session, go to the 2nd Session Options menu > Close 2nd Session (last option).
IMPORTANT: Any Settings (Hourline Displays, Project Views, Toolbox Settings etc.) done in the 2nd Session will not be saved. They have to be done in the main session. A warning window appears when closing the second session.