Source code of Tesseract's Releases.
Tesseract is included in most Linux distributions.
Downloads Archive on SourceForge. There you can find, among other files, Windows installer for the old version 3.02.
Currently, there is no official Windows installer for newer versions.
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Cygwin includes packages for Tesseract.
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UB Mannheim has installers available for version 3, 4 and current 5.0.0.Alpha.