We would like to find a freeware software tool which analyse besides the written code also the remarks in the code which replaces a Detailed Design document. (floating licenses).
What exactly do you mean by "analyse the code"? Are you looking for a free tool to reverse-engineer the code to some kind of UML representation? If so, you may try Doxygen. It supports many languages and can extract classes relations and even documentation if the code was properly documented to start with.
I my opinion, no tool is going to replace a detailed design document. Such document should explain the rational behind design decisions and trade-offs. It should also guide future developers to extend the software without breaking its structure. No automated tool can do this...