Ask HN: What new startups are creating products that are changing the world?

Slack is technically pretty boring, given that it's just hosted chat. But it's important because its adoption enables people to work remotely, which reduces long commutes, expensive housing, etc.

Twitter, Facebook, and YouTube are also technically boring but have had also had huge real-world effects.

What are some other newer startups that, like these, are having a big positive (or mixed) impact in people's daily lives?