Most cheeses (e.g. Cheddar) are made by pressing the cheese which allows the curds to set, while draining off the whey. Cottage cheese isn't pressed, so the whey remains and the curds stay soft.
In the same way that there are many types of Cheddar, there are different types of cream cheese. 'Philadelphia' is just a brand name.
Fromage frais is basically a Belgian/French variation of cottage cheese. However, cream is often added before sale, so that it is given the consistency of yoghurt. This makes it more suitable to serve as an accompaniment to a dessert ~ (try it with canned raspberries in syrup - DEVINE!) ~ but less suitable for use in a cheesecake.
This might be of interest:
http://www.philadelphia.co.uk/philadelphia1/pa ge?siteid=philadelphia1-prd&locale=uken1&Mid=& PagecRef=662
Chris