Some recollections from Reddit:
A bot that links the top posts of all time for a community. Gives a good sense of the community's greatest hits when referenced in discussions.
A bot that converts imperial to metric units or vice versa. Some people do find this one annoying, but as a metric user, this one helps me understand miles and pounds, etc.
A bot that summarises or pulls the first paragraph of a Wikipedia article.
Not to sound like one of those people, but a bidet. It hasn't eliminated my use of toilet paper, but certainly has reduced it, while leaving a squeaky clean feeling. I miss using it while away from home nowadays.
Other things are eye masks (I have sleep quality issues) and ereaders (never moving with ten boxes of books again).