Advice on PHP package

[Hfnet]

I am looking for a calendar app in php/mysql which can have restricted access, preferably open-source. I have a client who is a PA for other companies, so I want to provide a solution where people can see her availability but not who the other companies are, so if she is booked out for another company, the people see that she is unavailable, but they can see their own company details and recognise when she is doing work for them.

If anyone knows of an existing solution I would be very grateful.