To reproduce:
<ol>
  <li>Download the gist</li>
  <li>Install the pyttsx3 Python library</li>
  <li>
    Run the code normally.
    <pre><code>>python tts_test.py
It works</code></pre>
  </li>
  <li>
    Build with PyInstaller:
    <pre><code>>python -m pyinstaller tts.spec
Build exits without warnings or errors</code></pre>
  </li>
  <li>
    Run the executable:
    <pre><code>>dist\main\TTS_Test.exe
[13544] PyInstaller Bootloader 3.x
[13544] LOADER: executable is C:\Users\Alexandre\Desktop\tts_test\dist\main\TTS_Test.exe
[13544] LOADER: homepath is C:\Users\Alexandre\Desktop\tts_test\dist\main
[13544] LOADER: _MEIPASS2 is NULL
[13544] LOADER: archivename is C:\Users\Alexandre\Desktop\tts_test\dist\main\TTS_Test.exe
[13544] LOADER: No need to extract files to run; setting extractionpath to homepath
[13544] LOADER: SetDllDirectory(C:\Users\Alexandre\Desktop\tts_test\dist\main)
[13544] LOADER: Already in the child - running user's code.
[13544] LOADER: Python library: C:\Users\Alexandre\Desktop\tts_test\dist\main\python27.dll
[13544] LOADER: Loaded functions from Python library.
[13544] LOADER: Manipulating environment (sys.path, sys.prefix)
[13544] LOADER: sys.prefix is C:\Users\ALEXAN~1\Desktop\tts_test\dist\main
[13544] LOADER: Setting runtime options
[13544] LOADER: Initializing python
[13544] LOADER: Overriding Python's sys.path
[13544] LOADER: Post-init sys.path is C:\Users\Alexandre\Desktop\tts_test\dist\main
[13544] LOADER: Setting sys.argv
[13544] LOADER: setting sys._MEIPASS
[13544] LOADER: importing modules from CArchive
[13544] LOADER: extracted struct
[13544] LOADER: callfunction returned...
[13544] LOADER: extracted pyimod01_os_path
[13544] LOADER: callfunction returned...
[13544] LOADER: extracted pyimod02_archive
[13544] LOADER: callfunction returned...
[13544] LOADER: extracted pyimod03_importers
[13544] LOADER: callfunction returned...
[13544] LOADER: Installing PYZ archive with Python modules.
[13544] LOADER: PYZ archive: out00-PYZ.pyz
[13544] LOADER: Running pyiboot01_bootstrap.py
[13544] LOADER: Running pyi_rth_win32comgenpy.py
[13544] LOADER: Running tts_test.py
Traceback (most recent call last):
  File "C:\Users\Alexandre\Desktop\tts_test\tts_test.py", line 3, in <module>
    engine = pyttsx3.init()
  File "C:\Python27\lib\site-packages\pyttsx3\__init__.py", line 46, in init
    eng = Engine(driverName, debug)
  File "C:\Python27\lib\site-packages\pyttsx3\engine.py", line 52, in __init__
    self.proxy = driver.DriverProxy(weakref.proxy(self), driverName, debug)
  File "C:\Python27\lib\site-packages\pyttsx3\driver.py", line 77, in __init__
    self._driver = self._module.buildDriver(weakref.proxy(self))
  File "C:\Python27\lib\site-packages\pyttsx3\drivers\sapi5.py", line 22, in buildDriver
    return SAPI5Driver(proxy)
  File "C:\Python27\lib\site-packages\pyttsx3\drivers\sapi5.py", line 31, in __init__
    SAPI5DriverEventSink)
  File "C:\Python27\lib\site-packages\win32com\client\__init__.py", line 317, in WithEvents
    gencache.EnsureModule(tla[0], tla[1], tla[3], tla[4], bValidateFile=0)
  File "C:\Python27\lib\site-packages\win32com\client\gencache.py", line 524, in EnsureModule
    module = MakeModuleForTypelib(typelibCLSID, lcid, major, minor, progressInstance, bForDemand = bForDemand, bBuildHidden = bBuildHidden)
  File "C:\Python27\lib\site-packages\win32com\client\gencache.py", line 291, in MakeModuleForTypelib
    makepy.GenerateFromTypeLibSpec( (typelibCLSID, lcid, major, minor), progressInstance=progressInstance, bForDemand = bForDemand, bBuildHidden = bBuildHidden)
  File "C:\Python27\lib\site-packages\win32com\client\makepy.py", line 286, in GenerateFromTypeLibSpec
    gencache.AddModuleToCache(info.clsid, info.lcid, info.major, info.minor)
  File "C:\Python27\lib\site-packages\win32com\client\gencache.py", line 554, in AddModuleToCache
    mod = _GetModule(fname)
  File "C:\Python27\lib\site-packages\win32com\client\gencache.py", line 633, in _GetModule
    mod = __import__(mod_name)
  File "c:\users\alexan~1\appdata\local\temp\tmpcpltk4\gen_py\C866CA3A-32F7-11D2-9602-00C04F8EE628x0x5x4.py", line 10, in <module>
    import win32com.client.CLSIDToClass, pythoncom, pywintypes
  File "c:\python27\Lib\site-packages\PyInstaller\loader\pyimod03_importers.py", line 161, in load_module
    return self._importer.load_module(fullname, self._entry_name)
  File "c:\python27\Lib\site-packages\PyInstaller\loader\pyimod03_importers.py", line 396, in load_module
    exec(bytecode, module.__dict__)
  File "C:\Python27\lib\site-packages\pythoncom.py", line 2, in <module>
    import pywintypes
  File "c:\python27\Lib\site-packages\PyInstaller\loader\pyimod03_importers.py", line 161, in load_module
    return self._importer.load_module(fullname, self._entry_name)
  File "c:\python27\Lib\site-packages\PyInstaller\loader\pyimod03_importers.py", line 396, in load_module
    exec(bytecode, module.__dict__)
  File "C:\Python27\lib\site-packages\win32\lib\pywintypes.py", line 2, in <module>
    import imp, sys, os
  File "c:\python27\Lib\site-packages\PyInstaller\loader\pyimod03_importers.py", line 161, in load_module
    return self._importer.load_module(fullname, self._entry_name)
  File "c:\python27\Lib\site-packages\PyInstaller\loader\pyimod03_importers.py", line 396, in load_module
    exec(bytecode, module.__dict__)
  File "C:\Python27\lib\os.py", line 120, in <module>
    from os.path import (curdir, pardir, sep, pathsep, defpath, extsep, altsep,
ImportError: No module named path
[13544] Failed to execute script tts_test
[13544] LOADER: OK.
[13544] LOADER: Cleaning up Python interpreter.</code></pre>
  </li>
</ol>