If you want to quickly share your local website or local app running on localhost , or any service that listening on any local port and you want to expose , so anyone can access at that point ngrok saves the back . previously i used tool from Proggrium called localtunnel . it was awesome but ngrok has some more features and advantages .
its use secure tunnel to expose and you can capture all request traffic securely.

how to use

simple download for your platform from homepage of ngrok and open that zip and run ngrok

ngrok 80

use that  share your local web server listening on port (code)80(/code) , for example i shared port 3000 for my rails app . I started rails server to bind on 0.0.0.0 and port to 3000 then I shared that using ngrok

Ngrok Home Page : https://ngrok.com/