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: 
It's not Open Source, but other than that [OllyDbg](http://www.ollydbg.de/) might be what you are looking for. Other useful tools and information can be found on [www.openrce.org](http://www.openrce.org/).
You can look at Detours library from Microsoft Research. Its a generic API Hooking library.