selectively make contact groups silent At work , i would prefer to set my phone in such a way that only the calls from my family group will ring , while all other contact calls should be silent. And later i should be able to switch it back to normal.

In general , there are sound profiles for phones, but the profiles are not specific to a contact or a group, i need a work profile which will set Family - Normal Others - Silent . etc

Is there any app in the market that would help me with this??
If you use Tasker, you may be able to create a profile that will silent certain contacts during work hours.  Just a "heads up" - Tasker will require a little work to get it to work the way you would like for more complex tasks, but they have a very good community that will support you if you run into issues.