Hi,
I've seen here that that no namespaces are supported. Does it implies that I can't use an external C# framework ? like the good Aforge that I really need ?
If not, may is there a client-server workaround ? i.e. : unity program use my other software through connection
You could build your Aforge-using functionality into a dll plugin which you can then import into Unity. If you need all of Aforge, you would have to wrap it in its entirety within the plugin. Of course going from one system of managed code to another can be a bit tricky when you are treating it like it is unmanaged code.
You can use namespaces - they only won't work for your own objects that extend from MonoBehaviour (and I suppose similar Unity types). We use namespaces in our own code, and also external code that uses namespaces.