I'm a web developer for Limelight Department. I work with your typical web-based languages including: PHP, MySQL and jQuery. I prefer to build websites with WordPress, but have also created websites from scratch, sometimes with custom content management solutions.
I've also worked with many third party API's, typically using PHP and cURL to transport JSON requests. Some of these API's I am familiar with are: Facebook, PayPal, Authorize.Net, Paytronix and Mailchimp.
I am very experienced with WordPress and plugin development, although my plugins are currently for private use. You won't find any on WordPress.org (yet). Not because I can't or don't want to release plugins there, I just prefer to keep developments for our clients closed-source. They are usually very specific and are not regularly updated.
However I can proudly say that my plugins are usually better quality, more user-friendly, and more reliable than you would find on wordpress.org. Not all the time, but usually!