What are some alternatives?
When comparing concrete5 and ProcessWire, you can also consider the following products
WordPress - WordPress is web software you can use to create a beautiful website or blog. We like to say that WordPress is both free and priceless at the same time.
Drupal - Drupal - the leading open-source CMS for ambitious digital experiences that reach your audience across multiple channels. Because we all have different needs, Drupal allows you to create a unique space in a world of cookie-cutter solutions.
Joomla - Joomla! is the mobile-ready and user-friendly way to build your website. Choose from thousands of features and designs. Joomla! is free and open source.
Ghost - Ghost is a fully open source, adaptable platform for building and running a modern online publication. We power blogs, magazines and journalists from Zappos to Sky News.
SquareSpace - Squarespace is the easiest way for anyone to create an exceptional website. Pages, galleries, blogs, e-commerce, domains, hosting, analytics, 24/7 support - all included.
Grav - The modern open source flat-file CMS