Beyond the awesome OSS software it provides, Eclipse is the place to get dressed! As an evidence, here is my personal collection of Eclipse T-shirts gathered over the years of conferences, camps, Lynn bribing, etc.
Missing from this list: the long sleeves jeans shirts from eclipsecon 2007(?), the very first Eclipse hat from OTI/IBM, some GSoc shirts, and the EclipseCon exercise shirts, but I never got those because I'm usually too "tired" for the early runs.
With each of them come some good memories and I still wear them proudly :)