Top4 (also written Top 4) is a file compression utility for DOS, and associated file format. It was developed by Tobias Svensson / Topologi Software.
For v1.03 at least, the suggested file extension is .to4.
The v1.03 package includes a self-extracting executable maker, TOP4EXE v1.02, whose example commands use the extension .t4 for Top4 format.
Files begin with bytes
'T' '4' 0x1a.
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