Tapping the Send button accidentally can make for some embarrassing messages. Even worse is realizing as a message is being delivered that it's going to the wrong person. iOS has no way to stop the message or delay sending, until now. Enter the jailbreak tweak SendDelay.
Other tweaks such as DoubleCheck can help to reduce messaging errors, however SendDelay actually postpones message delivery. This creates a window of time during which the message can be stopped. As delivery is happening, the Send button actually turns into a Stop button, which can be used to stop sending.