I came across this recently. Looks like late 1980's vintage. Probably the diagnostic tool for the old L-series cars. I haven't tried it on my car yet, but it looks like it just reads and writes byte values by address over SSM0 or SSM1 protocol. It probably came with a list of important addresses.
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Subaru ECU and TCU Website
1992 Alcyone SVX Version L
1992 Alcyone SVX Version L
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1988 Subaru Justy J12 SL-II