Evan Selinger in The Atlantic:
Nudging is a distinctive way to help people make good decisions. It differs from the typical ways of attempting to change behavior: rational persuasion (e.g, providing new information), coercion (e.g., using threats to ensure compliance), adjusting financial incentives (e.g., paying students to get good grades) and bans (e.g., prohibiting smoking in restaurants). And, it has a limited domain of application: contexts where decisions need to be made, but we lack adequate time, information, or emotional wherewithal to know how to act in ways that further our best interests. In these cases, nudges work by subtly tweaking the contexts within which we make choices so that, on average, we will tend to make good ones.
Take ToneCheck, the emotional analogue to a spell checking tool. It is a nudge for those of us who can't resist sending flaming emails. Applying connotative intelligence research to “automatically detect the tone” of your email,” it offers the author a warning (that can prompt revision) if a draft exceeds the threshold for negative emotions (e.g., anger or sadness). The author has been nudged.