This i hope would be clearer. I am a convert from MS windows and now i am using linux (Ubuntu specifically). Emulators there is... i run windows based games, apps on my linux box and most of the common apps that are usually found in windows are almost, if not all has a linux counterpart or equivalent.
Here are some:
MS Windows                    Linux
MS Office                       Open Office
Limewire                       Frostwire/Limewire
Winamp                       Xmms
Photoshop                     Gimp
AIM, ICQ, MSN, Yahoo!, Jabber,
IRC instant messaging            Gaim
Word Pad (or notepad)Â Â Â Â Â Â Â Â Â Â Â Gedit/Kwrite
Windows Media Player            Totem
iTunes (for playing music)Â Â Â Â Â Â Â Â Â Â Rhythmbox
ID3 tag editor                   easytag
MIRCÂ Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Xchat
Premiere (Movie Editing)Â Â Â Â Â Â Â Â Â Â kino
Bittorado                      Bittorado
Dreamweaver                   Nvu
CDex                         Sound Juicer
Nero                          Gnomebaker/KB3
Outlook Express                 Evolution, Thunderbird
Snood                         Frozen-bubble
Partition Magic                  Gparted/QTParted
eMule                         aMule
Soulseek                       Nicotine
DC++Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Valknut
any multitorrent client             Azureus
any download manager           D4X or Gwget
regedit                        gconf
Adobe Illustrator                 Inkscape
Remote Desktop Connection        Terminal Server Client
Windows Explorer                Nautilus
Windows Picture and Fax Viewer    Image Viewer (Eye of GNOME)
Paint                          Jdraw
Those are the common apps that i think someone usually uses. Now if you really wanted to run the apps that run on windows to your linux box there is an emulator, WINE that can run any windows based apps to run on your linux box. Most of the popular games now also run on linux boxes. I actually run my Windows XP inside my Linux box. Linux being the host. ;D