EMu is a collections management system (CMS) used by many large natural history museums. A brief overview is provided by its parent company, Axiell, on their website.
EMu differs from other common CMS options in several major ways: (1) it is a for-profit business rather than a nonprofit or consortium-supported operation; (2) it is not open source; (3) it exists in myriad different customizations, based on the unique needs of each collection using it. Functionally, the first two differences can result in a lack of transparency and a slow response to fixing software issues, however they also mean that the museum has access to third-party support for maintenance and development of the CMS. The third difference means that two invertebrate paleontology collections at two different museums may have similar needs and processes but may be using two very different versions of EMu. For this reason, it is highly recommended to network with other EMu users and share best practices, issues, questions, etc. Consider joining the user community listserv.
A final difference is that EMu is built on a proprietary database engine called Texpress, which utilizes a nested relational rather than pure relational design. Doing so allows EMu to perform efficient searches and other operations on complex objects, such as large blocks of text. But it also means that data stored in EMu is much less normalized than in many similar CMS options, which necessitates careful design on the user end to ensure consistent, high-quality data.