Centering the navbar content in Bootstrap 4 (alpha 5)

Centering Navbar items is simpler in Bootstrap 4, and doesn't require additional markup.

<nav class="navbar navbar-expand-md navbar-light bg-faded">
  <ul class="navbar-nav mx-auto">
    <li class="nav-item active text-center">
      <a class="nav-link" href="#">Home <span class="sr-only">(current)</span></a>
    </li>
    <li class="nav-item text-center">
      <a class="nav-link" href="#">Features</a>
    </li>
    <li class="nav-item text-center">
      <a class="nav-link" href="#">Pricing</a>
    </li>
    <li class="nav-item dropdown text-center">
      <a class="nav-link dropdown-toggle" href="http://example.com" id="navbarDropdownMenuLink" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
        Dropdown link
      </a>
      <div class="dropdown-menu" aria-labelledby="navbarDropdownMenuLink">
        <a class="dropdown-item" href="#">Action</a>
        <a class="dropdown-item" href="#">Another action</a>
        <a class="dropdown-item" href="#">Something else here</a>
      </div>
    </li>
  </ul>
</nav>

Bootstrap 4 Center Navbar Demo (updated for v4.0.0)

If you need to center only specific elements, such as the Brand or Links, see this answer