Doing a rough research about .smt files, it is said that it belongs to a "Apollo Database Engine". Some other programs that uses it includes:

CAD Program SMT-circuit Layout
Creator Simulator (Symbol File) by Tufts University
HiPer-Six Memo File
IconAuthor (SmartObject)
QuickBooks by Intuit Inc.
SmartWare II Text File


*copy-pasta'd from filext.com