@echo off
set APP1=a.exe
set APP2=b.exe
set Pr=0
for /f "tokens=1 delims= " %%a in ('tasklist ^| findstr /i "%APP1% %APP2%"') do (
set APP=%%~a
set /a Pr+=1
)
if %Pr% equ 1 (
if /i "%APP%"=="%APP1%" start "" "D:\1.exe"
if /i "%APP%"=="%APP2%" start "" "D:\2.exe"
)
if %Pr% equ 2 start "" "D:\3.exe"
if %Pr% equ 0 start "" "D:\4.exe"
pause