Basic software's required for a PC to have a hassle free use:
Productivity: Microsoft Office 2013, OpenOffice, LibreOffice, Kingsoft Office,
Browsers: CoolNovo, Chrome, Firefox, Opera, Torch Browser
Instant Messenger (IM): Skype, Google Talk, Thunderbird, Outlook Express, AIM, Yahoo
Runtime support: Java, DotNet Framework, Air, Shockwave, Silverlight
Photo viewers: FastStone image Viewer/Editor, Picasa, Irfanview, Inkscape
PDF readers: Foxit reader cum printer, Adobe reader, Sumatra PDF
Antivirus: Avast, Avira, Microsoft Essentials, Kaspersky*
Remote Access: Team Viewer, Ammy Admin, CrossLoop
Developer tools: Filezilla, Notepad++, JDK, PuTTY
Online Storage: Dropbox, Google Drive, Sky Drive
Media Players: VLC, K-Lite Codecs, QuickTime
File Sharing: Bit torrent, µTorrent, DC++
*Kaspersky – Consumes more RAM & system resources which slowes down the PC performance
Software legend: Orange = Freeware / Open source , Blue = Demo / Limited edition