There are lots of open source and free applications which can be used uniquely or as an alternative to paid commercial applications. According to wiki,
Here is the list of 10 best open source applications of my choice. They are listed in random order. You can use them for free (as in “free speech” and also as in “free beer”).
VLC is a free and open source cross-platform multimedia player and framework that plays most multimedia files as well as DVD, Audio CD, VCD, and various streaming protocols. It is simple, powerful and fast. It plays most codecs with no codec packs needed, for example, MPEG-2, H.264, DivX, MPEG-4, WebM, WMV player, etc. It works on most platforms like Windows, Linux, Mac OS X, Unix. It in not only a media player but also media converter and streamer.
Home page : VLC
7-Zip is a free file archiver which is licensed under GNU LGPL License. It has high compression ratio in 7z format. For packing/unpacking it supports 7z, XZ, BZIP2, GZIP, TAR, ZIP and WIM file. Moreover it supports many files like ARJ, CAB, CHM, CPIO, CramFS, DEB, DMG, FAT, HFS, ISO, LZH, LZMA, MBR, MSI, NSIS, NTFS, RAR, RPM, SquashFS, UDF, VHD, WIM, XAR and Z for unpacking. For ZIP and GZIP formats, 7-Zip provides a compression ratio that is 2-10 % better than the ratio provided by PKZip and WinZip. Its other important features are strong AES-256 encryption in 7z and ZIP formats, self-extracting capability for 7z format, integration with Windows Shell, powerful File Manager, powerful command line version and plugin for FAR Manager.
Home Page : 7-Zip
Notepad++ is a free text editor and Notepad replacement that supports several languages. Running in the MS Windows environment, its use is governed by GPL License. Based on the powerful editing component Scintilla, Notepad++ is written in C++ and uses pure Win32 API and STL which ensures a higher execution speed and smaller program size. By optimizing as many routines as possible without losing user friendliness, Notepad++ is trying to reduce the world carbon dioxide emissions. When using less CPU power, the PC can throttle down and reduce power consumption, resulting in a greener environment.
Home Page : Notepad++
- Open Office
OpenOffice.org is the leading open-source office software suite for word processing, spreadsheets, presentations, graphics, databases and more. It is available in many languages and works on all common computers. It stores all your data in an international open standard format and can also read and write files from other common office software packages. It can be downloaded and used completely free of charge for any purpose.
Home Page : Open Office.org
Firefox is a free, open-source web browser for Windows, Linux and Mac OS X (and many other platforms) based on the Mozilla code base it is small, fast and easy to use. Firefox offers many advantages over Internet Explorer, such as tabbed windows, quick links, security and the ability to block ads. Firefox is well known for being the most customizable web browser. With a selection of thousands of free add-ons on the Firefox Add-ons site, you can customize Firefox to have it look the way that you want, and function the way that you want.
Home Page : Firefox
Thunderbird is a free open source graphical email client and newsreader developed by the Mozilla Foundation. It is available for Windows, Mac OS X, and Linux, includes support for both IMAP and POP email. It is cross platform and a strong contender of Microsoft Outlook and Eudora Mail. Like Mozilla Firefox, Thunderbird supports add-ons, extensions that provide additional functionality to the e-mail client. One of the key extensions available for Mozilla Thunderbird is Mozilla Lightning, an extension that adds calendar and personal information manager (PIM) capabilities to Thunderbird.
Home Page : Thunderbird
Audacity is a free cross platform audio editor. It allows you to record live audio, convert tapes and records into digital recordings, edit Ogg Vorbis, MP3, WAV or AIFF files, edit or mix sounds together, change the speed of recording, add effects and many other things. You can change the speed or pitch of a recording. It acts like a non-destructive editor, providing multiple levels of undo, but it also writes changes made to the audio to disk, eliminating the need for complicated real-time processing.
Home Page : Audacity
GIMP is an acronym for GNU Image Manipulation Program. It is a freely distributed program for such tasks as photo retouching, image composition and image authoring. It has many capabilities. It can be used as a simple paint program, an expert quality photo retouching program, an online batch processing system, a mass production image renderer, an image format converter, etc. It is expandable and extensible. It is designed to be augmented with plug-ins and extensions to do just about anything. The advanced scripting interface allows everything from the simplest task to the most complex image manipulation procedures to be easily scripted.
Home Page : GIMP
PDFCreator is an application for converting documents into Portable Document Format (PDF) format on Microsoft Windows. It works by creating a virtual printer that prints to PDF files, and thereby allows practically any application to create PDF files by choosing to print from within the application and then printing to the PDFCreator printer.
Home Page : PDFCreator
Instant messaging using application is not much popular nowadays but still Pidgin is surviving due to its consolidated chat service. It is an easy to use and free chat client used by millions. It lets you log in to accounts on multiple chat networks simultaneously. This means that you can be chatting with friends on MSN, talking to a friend on Google Talk, and sitting in a Yahoo chat room all at the same time.
Home Page : Pidgin