I've just started looking over your program, and while it looks very useful, it doesn't seem to be very accessible to assistive technologies, nor does it seem possible to interact with it to a very great extent using the keyboard. This creates problems both with accessibility for handicapped users, and with general efficiency of use for everyone.
The accessibility issues with the site mean that it may actually be illegal for government and public educational organizations to use your products. The quote below is from Section 508 of the Rehabilitation Act of 1973:
"Federal departments or agencies develop, procure, maintain, or use Electronic and Information Technology (EIT), they shall insure that the EIT allows Federal employees with disabilities to have access to and use of information and data that is comparable to the access to and use of information and data by other Federal employees." -
http://aboutwebaccessibility.com/home/law/publicFeng Office doesn't meet this standard.
One example of a problem that is caused by the way the site pages are currently structured is what happens when I attempt to use Voiceover to navigate in Safari. VO will take me to some of the buttons on the page, but it doesn't identify them, and it won't take me to any of the top navigation buttons ("Overview", "Notes", "Email", etc.).
Another issue, more related to efficiency of use than web accessibility, is that there doesn't appear to be any way to access pages such as "Tasks" using URLs. This seems like it should be a correctable problem, given that some links are "real" links, for example,
http://localhost/fengoffice/index.php?c=task&a=view_task&id=3 will take the user to the task whose id is 3. When I tried to use Firefox's iMacros plugin to automate this step, this failed as well.
If Feng Office were more accessible, it would also be easier to navigate it using the keyboard. There are many tools available to assist users with setting up shortcut keys, but to use them you first have to be able to access the interface elements. This may seem like a small issue, but as another user pointed out, small efficiency issues add up quickly when they're related to tasks you perform over and over again.
I think that it should be possible to make the application more accessible than it is currently, and I hope you will consider doing so going forward.
