SharePoint. Our entire Intranet and project management processes are rooted to SharePoint. It may work great in a homogenous Microsoft environment, but Linux and Mac users are screwed.
This is made worse by the fact that my MS-loving boss has bought into it completely and I was given the impossible task to make it work as a CMS for our websites. I felt so bad for every group we made sites for when asking if we could change how something looked/worked, because without lots of programming (outside my skill level), nope not really possible.
Pretty sure I will be leaving this job within the year despite how nice everyone is partly due to me being the one who gets stuck supporting this POS and I'm not a developer.