Surprisingly hard to find, the original version of TechTool Pro. This
is the only version of TechTool Pro that will work on the Mac Plus
(Version 2 will crash with an Unimplemented Trap). Included with this
upload is the 1.0.6 Install Floppies and the updater that will update
TTP to 1.0.7. (TTP2 Serial numbers will work with TTP1.) There's also
a demo of 1.0.

The release notes state that the changes made in 1.0.7 are as follows:

 * Added volume select panel to drive tests.
 * Added support for Mac OS 8.1 and HFS+.
 * Added support for Mac OS 8.1 era Macintosh Models.
 * Changes to splash screen noting TTP 2 release.
 * Bug fixes.

See also: [TechTool 1.x][1] (non-"Pro" version), [TechTool Lite 3.0.4][2] (freeware version)
Other Pro versions:

 * [2.1.1][3]
 * [2.5][4]
 * [3.0.1][5]
 * [3.0.3][6]
 * [3.0.6 & 3.0.9][7]
 * [4.0.2, 4.0.4, & 4.1.2][8]
 * [4.6.1][9]

Compatibility
Architecture: 68k PPC

For Macintosh Plus through iMac G3.
TTP 1.0.6: System 7.0 to Mac OS 8.0
TTP 1.0.7: System 7.0 to Mac OS 8.1

  [1]: http://macintoshgarden.org/apps/techtool
  [2]: http://macintoshgarden.org/apps/techtool-lite-304
  [3]: http://macintoshgarden.org/apps/techtool-pro-211
  [4]: http://macintoshgarden.org/apps/techtool-pro-25
  [5]: http://macintoshgarden.org/apps/techtool-pro-301
  [6]: http://macintoshgarden.org/apps/techtool-pro-303
  [7]: http://macintoshgarden.org/apps/techtool-pro-306
  [8]: http://macintoshgarden.org/apps/techtool-pro-402
  [9]: http://macintoshgarden.org/apps/techtool-pro-461-ppc-g3g4g5