HubSpot - Cambridge/Boston, MA - <a href="http://www.hubspot.com" >
HubSpot is a great place to work.  In fact, it was ranked the #2  place to work in Massachusetts and we're the fastest growing non-public software company in the US (and 33rd fastest growing non-public company).  We focus on helping businesses with their online marketing - specifically helping them to avoid interrupting and annoying their customers with bad marketing.
In Engineering, we're organized into small teams where you get to have a big impact on the product.  We have a great environment to move quickly in and deploy hundreds of times a day.  We use GitHub Enterprise for SCM, Jenkins to build, an internal deployer system for zero-downtime deploys, and we even have a Heroku-style system coming (for those that would ask "why not just use Docker?", there's still the provisioning and routing issue).
On the backend, we use Java and Python (though more Java these days).  It's really modern Java.  We use Dropwizard which is really wonderful if you haven't checked it out (annotate paths similarly to how you'd use Flash in Python and just have the method return an object and Jackson will serialize it into JSON and return it - Java can be really nice).  For data, HBase, Hadoop, MySQL, ZoopKeeper, Redis, and Memcached all have their place.  Again, we deploy hundreds of times a day so don't expect your code to languish in the repository.  We like pushing small changes fast.
On the front end, we use Backbone.js, CoffeeScript, and jQuery.  We also have our iPhone and Android applications.
Engineers get a lot of responsibility from the start and you'll usually push changes your first day.  You'll also get a Retina MacBook Pro and Thunderbolt display.
Work schedules are flexible.  Most engineers keep a 10-6 schedule.  You get to make a meaningful difference in a product with loads of paying customers and a ton of traffic.  Best of all, you get to work with loads of smart and fun people.  That's the best thing about HubSpot: the people are great people that you can rely on, learn from, and have a great time getting things done with.
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