We use a combination of the industry’s best tools for WordPress development including hosting our sites on WP Engine.

We manage about 25+ sites for our clients so we like to use ManageWP to make sure all plugins and core are up to date often.

As for overall project management? We like Basecamp and/or Trello combination.

We also use Bitbucket and Github for code repos.

And finally we use our UXDesignKit.com library to help with early User Experience design research on our products/services.