MDB is the format used by Microsoft Access, one of the most popular databases in the world. Usually, a front end application of some type is used to--no pun intended--access the data. However, it can sometimes occur that you end up with a "naked" MDB and no way to peek inside it. Enter MDB Viewer Plus (free).
MDB Viewer Plus is a lightweight (no fancy install, just extract the executable) program which can be easily stowed on a USB key.
The article continues at http://www.pcworld.com/article/168319/mdb_viewer_plus_lets_you_view_microsoft_database_files_without_access.html