The Action Network is a progressive online organizing platform. Anyone can become an organizer by creating a free account.
With that account, organizers can publish actions to the public, such as a petition to an elected official, an event RSVP form for a meeting the organizer is holding, a survey form to collect answers from a community, a fundraising form to collect money for an upcoming campaign, a ticketed event page to sell tickets to an event, or a letter campaign to have activists email elected officials.
As other activists take action and fill out the forms an organizer has published, those activists are opted in to the organizer's email list. Using the built-in mass mailing tool, organizers can contact that list of activists whenever they want, and download the data on their list too!
In short, the Action Network includes everything you need to organize online, using software similar to what the Obama campaign used in 2008 and 2012 to build and manage their email list.
This training by Action Network covers the basics on how to use their tool set, including setting up your account, sending bulk email, setting up forms, creating engagement ladders, among other skills.