Other forms: kangaroo courts
A kangaroo court is an unlawful, false court that doesn't follow the legal standards agreed to by the community.
While a kangaroo court might appear to be devoted to law and justice, in most cases the outcome of a case tried in such a court is decided long before proceedings start. You might guess that the phrase is Australian in origin, but it seems to have started in Texas. The "kangaroo" may have referred to Gold Rush era claim jumpers — miners who illegally took other people's land claims and were then tried in one of these quick, mock courtrooms.