Group Leads is an interesting browser extension (Chrome and Firefox at the moment) that allows its users to turn any new Facebook Group member to an email list subscriber without having to spend on creating a Facebook ad.
Not only are you able to grow your list from your Facebook group with this smart app. You are also able to get new group members data posted automatically to a Google Sheet for further processing.
If you are running a Facebook group, this may be a piece of gold for you, given the importance of collecting and storing email addresses of your community members where you have full control.