C++
Microsoft Access was developed on C#. Source: MSDN (Microsoft Developer Network)
Microsoft Windows is mainly programmed in C++ and C.
Robert Lafore has written: 'Object-oriented programming in Microsoft C++' -- subject(s): Object-oriented programming (Computer science), C++ (Computer program language), C. 'Microsoft C. Programming for the I.B.M.Personal Computer' 'Object-oriented programming in C++' 'Windows Programming Made Ridiculously Easy Book' 'The Waite Group's C Programming Using Turbo C++ (The Waite Group)' 'Microsoft C programming for the IBM' 'The Waite Group's Microsoft C programming for the PC' -- subject(s): C (Computer program language), IBM microcomputers, Microsoft C (Computer program), Microsoft C., Programming
It's possible that Excel was written in C.
Robert G. Crawford has written: 'Microcomputer programming with microsoft BASIC' -- subject(s): BASIC (Computer program language), Microcomputers, Programming
Michael A. Vine has written: 'Microsoft Access VBA programming for the absolute beginner' -- subject(s): Microsoft Access, Microsoft Visual Basic for applications, Database management 'C programming for the absolute beginner' -- subject(s): C (Computer program language)
Ross P. Nelson has written: 'Microsoft's 80386/80486 programming guide' -- subject(s): Assembler language (Computer program language), Intel 80386 (Microprocessor), Intel 80486 (Microprocessor), Programming
James Perotti has written: 'QuickBASIC business programming' -- subject(s): BASIC (Computer program language), Business, Computer programs, Microcomputers, Microsoft QuickBASIC, Programming
Mark Walmsley has written: 'Programming in Java' 'Graphics programming in C++' -- subject(s): C++ (Computer program language), Computer graphics, Microsoft Windows (Computer file) 'Internet Programming in C++'
Paul S. Cilwa has written: 'Windows programming power with custom controls' -- subject(s): C (Computer program language), C++ (Computer program language), Microsoft Visual BASIC, Microsoft Windows (Computer file) 'Windows 95 programming with custom controls' -- subject(s): C (Computer program language), C++ (Computer program language), Microsoft Windows (Computer file), Operating systems (Computers)
Word is mostly written in C++. It also contains a programming language which is Visual Basic for Applications, which is an implementation of Microsoft's Visual Basic 6. Search Wikipedia for more info.
PHP is written in the C programming language.