I am compiling a list of freeware tools that can do almost everything you want to do on your computer. Leave comments if you think i missed something.

Office

OpenOffice – This one is the best alternative to Microsoft office suite majority of us are used to. Give it a try and its worth the money. Its free no money needed though but do almost everything that microsoft office suite does.
AbiWord – Its a decent Text editor for your small needs. Its not as comprehensive as Microsoft Word or open office word replacement but decent enough for many people.
Adobe Reader – Every one knows this though. Its the free reader that Acrobat provides for reading PDF files.
Foxit PDF Reader – Another PDF reader, an alternative to adobe reader and its much lighter.
PDFCreator – A tool used to create pdf documents from other formats.
Sunbird – Its a calendar/organizer good enough for all your needs.
EssentialPIM Free – Another  calendar/organizer.

Archive managers

7-Zip – A free compression program more than good enough for personal use and do all that commercial compression products do.

Internet

Firefox – A web browser thats almost on the verge of replacing Internet explorer  from No.1 position soon.
Maxthon – Another decent web browser.
Opera – Another light weight web browser offering tons of functionality.
Thunderbird – A email client good enough to replace outlook express or outlook.

Free Download Manager – A download manager good enough for downloading stuff fast using multiple connections.
FlashGet – Another free  download manager
HTTrack – A offline browser or website copier letting you download whole website on your hard disk.
RSSOwl -  A great RSS reader.

P2P

µTorrent -A torrent client.Most light weight and widely used for downloading stuff using torrent technology.
Azureus – Another torrent client but a bit heavier one.
BitComet – Another torrent client.
PeerGuardian – A IP blocker used to block connections from certain IPs while you download using torrent clients.

Chat

Live Messenger – Popular IM client from Microsoft.
Yahoo Messenger – Another chat client from yahoo.
Pidgin – chat client
Skype – VOIP client used for PC to PC and PC to Phone talks.
Google Talk - VOIP client from google.

Security

AVG Free – Most popular free antivirus from AVG.
Avast Home Free – Another free antivirus from avast providing good enough protection for home users.
AntiVir PersonalEdition – Another free antivirus from Avira.
BitDefender Free – Free antivirus from Bitdefender but not with a real time protection.
Ad-aware – Most popular anti-spyware used for protecting your system.
Spybot: Search & Destroy – Another anti-spyware providing good security from spywares
Windows Defender – A anti-spyware offered by Microsoft bundled along with Vista and Windows 7. Can be installed on Windows XP too.
ZoneAlarm -The best firewall offered by Zonealarm.
Simple File Shredder – IT is used for securely deleting  files.

Audio

WinAmp – The most widely used audio player. A small and great tool for playing audio.
JetAudio – Another audio/video player having some great functions.
XMPlay – audio player

Video

TheKMplayer – The best media player ever i came across.
VLC – Another video player having great features including broadcasting options.
Media Player Classic – Small but great video player
Zoom Player – video player
GOM Player – video player

VirtualDub – video editor
CamStudio – video screen recording
AviSplit – Avi splitter
Video mp3 Extractor – rip audio from video files
Free iPod Converter – convert all popular video formats to iPod video

Image

Gimp – The best replcaement for Photoshop as image editor.
Paint.net – Another great image editor
IrfanView - image viewer
Picasa - image viewer
WinSnap – screen capture

3D

Blender3D – 3D renderer
Maya Learning Edition – 3D modeling

CD/DVD

Burnaware -Excellent replacement for NERO.
CDBurner XP Pro – CD/DVD burner
ImgBurn – ISO, BIN burner
Daemon tools – virtual CD/DVD
DVD Decrypter – DVD ripper
DVD Shrink – DVD ripper

Codecs

GSpot – codec information
AC3Filter – audio codec
Xvid – video codec
QuickTime Alternative – video codec
Real Alternative – video codec
K-Lite Codec Pack – all codecs

System Ulilities

CCleaner – system cleaner
xp-AntiSpy – OS setup
jv16 Powertools – system utilities
Unlocker – file eraser
Eraser – secure file eraser
Undelete Plus – file recovery

MozBackup – backup and restore bookmarks, etc.
SyncBack – system backup
Java Runtime Environment – java for Windows

UI Enhancements

RocketDock – application launcher
LClock – Windows Longhorn clock
Y’z Dock – application launcher
Microsoft TweakUI – system settings
BricoPacks – shell packs
ShellPacks – shell packs
XPize – GUI enhancer
Vista Transformation Pack – complete visual style
Vista Sound Scheme – Windows Vista sound scheme
Royale Theme – visual style theme for windows XP

Miscellaneous

nLite – Build your own custom Windows XP disk.
VirtualPC – create virtual machines
Windows Live Writer – WYSIWYG blog writing right from your desktop