Windows/Mac/Linux: You've got plenty of choices for app launchers, but if you don't mind getting your hands messy and adding your own features, Zazu is an app that's worth a look.
Zazu comes packed with just a small handful of basic features that pretty much every launcher has these days, like the ability to find applications, run system commands, search online or run basic calculations. More interesting is the ability to add plugins, which can do stuff like search 1Password for passwords and toggle your VPN. You can, of course, also make your own plugins if you're technically inclined. We've certainly seen similar apps before, like Lacona or Flashlight, but since Zazu is cross-platform, we might see more plugins pop up for as time goes on.