Windows equivalent of whereis?

The where command does what you want and goes back at least to the resource kit for Windows 98, and is included by default in Server 2003, Vista, and newer:

C:\>where csc
C:\Windows\Microsoft.NET\Framework\v3.5\csc.exe
C:\Windows\Microsoft.NET\Framework\v2.0.50727\csc.exe

If executed with no arguments (on Vista), it results in one of my favorite messages:

C:\>where
ERROR: The operation completed successfully.

If executing in PowerShell, be sure to include '.exe' to distinguish from any 'where' aliases or scripts along the path. ('where' is a typical alias for Where-Object.ps1)

C:\> where.exe where.exe
C:\Windows\System32\where.exe

Please, use where command:

> where app.exe

It is the best way to achieve your goal.

You can also use PowerShell command:

> $env:path.Split(';') | gci -Filter app.exe

and expanded version looks like this:

 > $env:path.Split(';') | select -Unique | ? {$_ -and (test-path $_)} | gci -Filter app.exe

hackerish which.cmd:

@echo off
@set PATH=.;%PATH%

@rem 
@rem about:  something similar like the unix-alike-which, but with
@rem         within pure cmd
@rem 

if "%1" == "" (
    @echo Usage: 
    @echo.
    @echo   which 'cmd'
    @echo.
    @echo.if 'cmd' is not found, ERRORLEVEL is set to 1
    @echo.  
) else (
    ( @for %%f in (%1 %1.exe %1.cmd %1.bat %1.pif) do if not "%%~$PATH:f" == "" ( @echo %%~$PATH:f ) else @set ERRORLEVEL=1) 
)

Somewhere "out there" I found this batch file whereis.bat:

@for %%e in (%PATHEXT%) do @for %%i in (%1%%e) do @if NOT "%%~$PATH:i"=="" echo %%~$PATH:i

Update: maybe I found it here.