When we need to keep data in a safe place, we turn to PostgreSQL. Not only is the software rock-solid, but new versions add amazing features like JSON support that give us the best of both worlds: SQL and NoSQL.
React is amazing for applications that have a lot of moving pieces. The underlying abstraction makes it easy to keep track of highly stateful UIs while keeping code complexity down, so we don't spend as much time fixing bugs.
We like to go native with iOS development, and Objective-C has been the only game in town until recent introduction of Swift. We're keeping an eye on Swift, but we aren't giving up on the [old way:to do:things]!
We turn to Sidekiq when we need to run background jobs in a Rails app, which we do for just about every Rails app we write. We especially like the ops tools that come with Sidekiq, which make it easy to monitor and maintain.