Yes, NationBuilder is a newer service. If you are concerned about that, or have to convince the "powers that be" at your organization that we are legit, here is what you can tell them.
We are an incredibly experienced and committed team, who have built several companies and non-profits from the ground up. Our parent company, 3dna, was founded in 2008 and includes other products such as the popular Twitter petition site act.ly. The engineers and organizers behind NationBuilder have deep and rich experience in software development, tech company management, journalism, film production, government and cause organizing. You can read more about us here.
NationBuilder is also well-funded with backing from venture capital firm Andreessen Horowitz, Facebook's first president, Sean Parker, and Facebook co-founder Chris Hughes. We are committed to growing our essential organizing toolkit long into the future, and are growing a large network of designers, developers and consultants who share our vision.