As mentioned already, many non-US airlines have 7-10kg limits.

In my experience most of the time as long as carry on is small and doesn't look heavy there is no attempt to weigh it. If weighed by check in or gate staff and slightly over limit generally no problem.

Problems arise at airports where airport staff check carry ons (typically just before immigration or security) because they'll enforce strict limits (although sometimes waived for first/business class passengers).