Softphone and Call Manager

We are in the process of swapping on to Asterisk from Zuktys. The Zultys system uses a phone manager which can be used to do a lot of the functionality that the phone can do, like call transfer, DND, parking etc. It also acts as a softphone when it is not bound to a physical phone.

Does anyone know if there is anything like this available or being developed at the moment? Or is there an OSS softphone that we can get developed?

We are aware of the softphones, and I have tried the XLite one, but we wnat to be able to do a lot more.
Any advice or help would be much appreciated.