Question: Does anyone know tools like [SpyStudio](http://www.nektra.com/products/spystudio/) to hook processes?
The features I would like to have are:

* log function calls on other processes
* GUI
* scriptable
* opensource

I already looked at some tools like:

* [SpyStudio](http://www.nektra.com/products/spystudio/)
* [Detours](http://research.microsoft.com/sn/detours/)
* [DynInst](http://www.dyninst.org/)

but none really fully satisfies me.

Answer: 
You can use [Deviare](http://www.nektra.com/products/deviare/) from the same company that've developed SpyStudio. It lets you hook COM Interfaces.
[SpyStudio](http://www.nektra.com/products/spystudio/) uses this API to monitor functions. It has a database of types that lets you get/set parameter values of any type.
You can look at Detours library from Microsoft Research. Its a generic API Hooking library.