The chat app, which is run by a nonprofit foundation, has been downloaded 220 million times. Here’s what to know about Signal, including who owns it and whether it’s safe to use.

Vast swaths of the subway still rely on signal equipment from the Great Depression. A multibillion dollar plan, now at risk, ...

A team of over 150 scientists has achieved what once seemed impossible: a complete wiring and activity map of a tiny section ...