[xboxnolifes]

Nadeko bot is a fairly big bot that has the ability to configure custom responses that the bot will reply with if a user types a certain message (any string of text, no prefix).

Core functionality is of course behind a prefix, but that's just convenient.

[anilakar]

Another popular bot, Mudae, allows the user to use both prefixed commands and slash commands, and the latter can take a few seconds to go through. Not acceptable when you have to fire ten or more commands at once in under half a minute.