I recently had an excellent opportunity to participate at one of our customers' Hack Day events. I had never heard of HackDay prior to my experience last week, but it turned out to be a lot of fun. The concept is simple - give a room full of developers 24 hours to "hack something together" - usually related to the company's business, or work the company is doing - to be demonstrated at the end of the 24 hour period. The demo should last 90 seconds or less, and you need to be clear about what bits were hacked together during the 24 hours, and what bits you brought it. You can use any technology you want, and it isn't expected to be pretty - just hacked together with some sort of purpose.
This company (who I'm not sure I can say the name) held theirs last Thursday and Friday, and had about 70 developers participate. The hacks ranged from updates of functionality to some Green Screen apps to some Flash and Silverlight work (one guess at who hacked together the Silverlight bits...) These events are usually kept to internal company employees only, so it was a real privilege to be invited as an outsider to this one.
I think that holding your own HackDay is a fantastic thing for companies to do - not only does it give the company's developers a chance to stretch their wings on some technology that they've been wanting to try, but it also results in some creative ideas that lead to the development of new applications that their customers often find very valuable. According to a spokesman for this company, several of the hacks from last year's event have made their way into the various products this company produces! That is a great testament to the developers at this company, for their creative ideas, but also to these companies for showing their faith in their development staff to develop some great software.
Let me know when you're holding your Hack Day - I'd love to come out and visit!