Popular Open-Source Alternatives

[Bink]

I was asked to create this sticky, but it's something I'd also been thinking about doing for a while, being the open-source advocate I am. The ones I'll initially list are ones I've personally tested against other software and continue to use.

• SourceForge - Comprehensive directory of open-source projects.
• WEBI.ORG - Free and Open Source Software Directory.
• Open Source Alternatives - Find open source software alternatives to well-known commercial software.
• AlternativeTo - Provides a large list of open-source and other alternatives to popular commercial software.

Desktop Applications

• LibreOffice - Office suite
• OpenOffice - Office suite.
• Notepad++ - Fully featured text editor with syntax highlighting.
• PDFCreator - PDF creation software.
• Electric Sheep - Psychadelic screensaver.
• InfraRecorder - CD/DVD burning software.
• StarDict - Cross-Platform and international dictionary Software. It has powerful features such as "Glob-style pattern matching", "Scan selection word," "Fuzzy query," etc.

Internet Browsers / Email Clients

• Mozilla Firefox - Extremely popular web browser, made very personalised and modular by the availability of extensions.
• Mozilla Thunderbird - Email client, made very personalised and modular by the availability of extensions.
  • Lightning extension, for Thunderbird/Sunbird - Provides a calendar for Thunderbird/Sunbird (like Outlook).
  • Provider for Google Calendar, for Thunderbird/Sunbird - Allows Thunderbird/Sunbird to read and write events to Google Calendar.
• Mozilla SeaMonkey - Web-browser, advanced e-mail and newsgroup client, IRC chat client, and HTML editing made simple.

FTP Clients

• FileZilla

Download Managers

• eMule - ED2K, Source Exchange and Kad client.
• Azureus - Highly featured BitTorrent client written in Java.
• Cabos - Gnutella file sharing program based on LimeWire and Acquisition.
• HTTrack - Allows you to download websites maintaining HTML and images, etc.
• Free Download Manager - Download/upload manager, accelerator that supports HTTP, FTP, BitTorrent and Flash video.

Instant Messangers / VoIP

• Pidgin (previously Gaim) - AIM, Bonjour, Gadu-Gadu, Google Talk, Groupwise, ICQ, IRC, MSN, MySpaceIM, QQ, SILC, SIMPLE, Sametime, XMPP, Yahoo! and Zephyr networks.
• aMSN - Highly featured MSN clone.
• OpenWengo - VoIP software that lets you enjoy free calls, video conferencing, SMS and chat over many existing protocols (MSN, AIM/ICQ, Yahoo!, Jabber).
• SIP Communicator - Audio/video Internet phone and instant messenger that supports popular instant messaging and telephony protocols such as SIP, Jabber, AIM/ICQ, MSN, etc.

Image Manipulation / 3D Animation

• The Gimp - Photoshop Equivalent.
• Scribus - Desktop publishing. Equivalent to InDesign and QuarkXPress.
• Inkscape - Vector illustration, equivalent to Illustrator, Freehand, Corel Draw and Xara X.
• Paint.NET - Paint.NET is free image and photo editing software.
• Blender 3D modeling/animation software.
• POV-Ray - 3D modeling/animation software.

Video Tools

• FFmpeg - Video conversion utility.
• MediaCoder - Universal batch media transcoder.
• VirtualDub - Basic editor, featured encoder.
• VirtualDubMod - Basic editor, featured encoder.
• HandBrake - DVD to MPEG-4 converter. Outputs to MP4, MKV, AVI or OGM.

Sound Editors / Rippers / Compression Tools

• Audacity - Full featured sound editor.
• CDex - CD audio extraction and audio conversion.
• LAME mP3 Encoder (download) - Highest quality MP3 codec.
• RazorLame (LAME front-end)

Compression & Backup

• 7-Zip - Packs: 7z, ZIP, GZIP, BZIP2 and TAR. Unpacks: RAR, CAB, ISO, ARJ, LZH, CHM, Z, CPIO, RPM, DEB and NSIS.
• Cobian's Backup - Highly featured scheduled backup software, which supports a lot of features normally only found in commercial backup solutions.

Media Players

• MediaPlayerClassic - With the right codecs, will play virtually anything and everything.
• VLC Media Player - Natively supports a large range of video formats.
• MPlayer - Natively supports a large range of video formats.
• Songbird - Desktop Web player, a digital jukebox and Web browser mash-up.
• aTunes - Audio player and manager.

Network Administration

• Wireshark - Network analyzer previously known as Ethereal.
• TightVNC - Simple remote access.
• Ultr@VNC - More featured remote access.
• Open Kiosk - Kiosk management system suited for use in controlled computing environments such as public access systems, libraries, school computer laboratories and internet cafes.
• Putty - Telnet/SSH client.
• OCS Inventory NG - Automated network inventory and deployment system.
• Nmap - Network exploration or security auditing (port scanner).
• BO2K - Remote control of systems, including network, registry, passwords, file system, and processes. Based on Back Orifice.

System Tools

• ClamWin Free AntiVirus - (doesn't support on-access scanning yet)
• Clonezilla - Drive cloning (like Ghost) and system deployment.
• Partition Logic - Hard disk partitioning and data management.
• Rufus - A small utility that helps format and create bootable USB flash drives, such as USB keys/pendrives, memory sticks, etc.
• Synergy - Share a single mouse and keyboard between multiple computers with different operating systems, each with its own display, without special hardware. Imagine the functionality of dual monitors (expanded desktop) except each monitor is connected to a different computer.

Security

• Darik's Boot and Nuke - High security drive wiping.
• Eraser - Delete files securely off your hard drive utilizing DoD standards.
• Extended Password Generator - Generates pronounceable and random passwords.
• PGP (Pretty Good Privacy) - Encryption package.
• TrueCrypt - On the fly encryption. Supports volume encryption.
• Waste - Secure P2P.
• KeePass - Password Manager.
• DCFirewall - A rule based packet and application filtering firewall.

Personal Finance

• TurboCASH - For managing personal finance.
• Quasar - Accounting package.

Games / Simulators

• The Ur-Quan Masters (StarControl II remake)
• The Bub's Brothers (Bubble Bobble remake)
• Frozen Bubble (requires ActivePerl 5.6.1 and SDL_Perl)
• Scorched 3D (3D remake of classic Scorched Earth)
• Racer
• TuxRacer
• FooBilliard
• Open Transport Tycoon Deluxe - (OpenTTD) Transport Tycoon Deluxe remake.
• Celestia - Free space simulation that lets you explore our universe in three dimensions.
• Stellarium - Stellarium is a planetarium that shows a realistic sky in 3D, like you would with the naked eye, binoculars or a telescope.