Hello Guys,
I am looking for feature which some online editors has (gliffy.com etc.). What I am looking for is some kind of "elastic line". For example, imagine two rectangles connected with this "elastic line" which will stretch when you will move one of rectangles.

Many thanks

OK, I have it done partially. The diagram conenctors (ctrl+F2) is the simmilar tool what I was looking for. It would be great if it can make nodes and allowing another shape not only straight line.

Yep, that's the only connector you can have.

It has been discussed quite often. At the end, Inkscape is not a diagram drawing app and the devs have other priorities/ideas for the product.

It would be great... but nope.

I'm not entirely clear what you're asking. But any line can be "elastic" if you make your selections properly. Although the rectangle would need to be converted to a path. In the case of 2 rectangles connected by a line, you would need to select 1 rectangle, and the path. Switch to Node tool, then do Ctrl + A, which selects all the nodes. Then hold Shift key, and click the node that you don't want to move (which deselects that node). Now you can grab any of the highlighted nodes and drag the rectangle with one end of the line.