The last version to officially support 32-bit (x86) Windows is calibre 5.44.0 . You can find this and other versions in the Previous calibre releases archive .
The calibre release index provides a comprehensive list of every version ever released. Look for installers ending in win32.msi for x86/32-bit systems. calibre x86 download
Even on older x86 hardware, calibre remains the "one-stop solution" for ebook needs. It allows you to: Change EPUBs to MOBI or AZW3 for Kindles. The last version to officially support 32-bit (x86)