Digitrax DB210 All Scale Advanced Loconet Booster.  Up to 8 Amps of power.  AutoReversing

If you're looking at this you probably already know what it is.  And what it's used for and how to hook it up, so you probably don't need the instruction sheet.  Which is good because I can't find it, if there ever was one. A full description and installation instructions are available on the Digitrax web site and you can even print them out if you need a paper copy.

I do know that it was purchased new and tested but never installled.