the only thing this sim does not have is the ability to move the fulcrum of the blue lever bar (limited to middle). HINT: the ends of the grey bar can be moved, to change behaviour or to keep the simulation in view.

...And the sim doesn't like excessive acceleration (but because of that, it can indicate the forces exerted). The grey bar length can replace the need to adjust the fulcrum.

animation seems to have some mistakes. center of the blue arm becomes sometimes not fixed anymore, but floating by the lenght of the blue arm

where it is used??? give some example

Isn't this linkage Chebyshoff's Lambda-linkage? Wikipedia shows other one for Hoecken's.

I don't see any animation at all. The screen is simply blank. What happened?

You should have adobe flash player in order to see this animation.