A landlord lowering rent in tough financial times. Able-bodied neighbors delivering canned goods to an elderly couple who can’t leave their home. Neighbors trading cat food for hand sanitizer. Organized groups clanging together pots and pans at night to show their support for health care workers and first responders. A dog lover walking pups for those who need it. These are all true stories that have taken shape on the social networking service Nextdoor over the last several days, showing the heartwarming, smile-inducing power of this global platform.