Free and Open Source

Easily format and create bootable USB flash drives, such as USB keys/pendrives, memory sticks, etc.
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WinCDEmu is an open-source CD/DVD/BD emulator - a tool that allows you to mount optical disc images by simply clicking on them in Windows Explorer. If you have downloaded an ISO image and want to use it without burning it to a blank disc, WinCDEmu is the easiest way to do it.

Features:

• One-click mounting of ISO, CUE, NRG, MDS/MDF, CCD, IMG images.
• Supports unlimited amount of virtual drives.
• Runs on 32-bit and 64-bit Windows versions from XP to Windows 10.
• Allows creating ISO images through a context menu in Explorer.
• Small installer size - less than 2MB!
• Does not require rebooting after installation.
• A special portable version is available.
• Translated to more than 20 languages.
• Does not occupy drive letters when not used.
• Supports data, DVD-video and BD-video images.
• WinCDEmu is free for any kind of use - it is licensed under LGPL

Translations:
WinCDEmu supports various UI languages through the LNG files maintained by the community. You can download the latest language files or submit your own translation in the Online Translation System.

Free and open source program uninstaller. Can remove large amounts of unwanted applications quickly. .

BleachBit deletes unnecessary files to free valuable disk space, maintain privacy, and remove junk.

Rid your system of old clutter including cache, cookies, Internet history, localizations, logs, temporary files, and broken shortcuts.

Designed for Linux and Windows systems, it wipes clean Adobe Acrobat Reader DC , APT, Bash, Beagle, Chromium, Epiphany, Mozilla Firefox, Flash, GIMP, Google Chrome, Google Earth, Internet Explorer, Java, KDE, OpenOffice.org, Opera, RealPlayer, Safari, Second Life viewer, Skype, VIM, XChat, Yum, and more.

BleachBit has never bundled any junk like browser toolbars.

7-Zip is a file archiver with a high compression ratio.

The main features of 7-Zip

High compression ratio in 7z format with LZMA and LZMA2 compression
Supported formats:
Packing / unpacking: 7z, XZ, BZIP2, GZIP, TAR, ZIP and WIM
Unpacking only: AR, ARJ, CAB, CHM, CPIO, CramFS, DMG, EXT, FAT, GPT, HFS, IHEX, ISO, LZH, LZMA, MBR, MSI, NSIS, NTFS, QCOW2, RAR, RPM, SquashFS, UDF, UEFI, VDI, VHD, VMDK, WIM, XAR and Z.
For ZIP and GZIP formats, 7-Zip provides a compression ratio that is 2-10 % better than the ratio provided by PKZip and WinZip
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
Plugin for FAR Manager
Localizations for 87 languages

7-Zip works in Windows 10 / 8 / 7 / Vista / XP / 2012 / 2008 / 2003 / 2000 / NT. There is a port of the command line version to Linux/Unix.

A free and open source password manager that keeps all of your passwords safe in one place.

LibreOffice is a powerful office suite – its clean interface and feature-rich tools help you unleash your creativity and enhance your productivity.

GitMind is a free online mind map maker for brainstorming, project planning, development, action, and other creative tasks. This tool lets you share mind maps with tons of users and collaborate with them. GitMind's mission is to become the leading global platform for digital content in order to enable customers to do their jobs with maximized productivity, little effort and minimal time.

Free email application that’s easy to set up and customize - and it’s loaded with great features!.

Mozilla Firefox (known simply as Firefox) is a free and open source web browser descended from the Mozilla Application Suite. Firefox is highly extensible, with thousands of third-party add-ons available.

Firefox version 60+ (Quantum) is presently faster than Google Chrome and use less memory than Chrome. Compare to previous versions of Firefox, the Quantum version is twice as fast, promote parallelism, and has more intuitive user interface.

Security-focused VPN developed by CERN scientists from the ProtonMail team. Enabling Internet without surveillance.

FDM accelerates downloads by splitting files into sections and then downloading them simultaneously.
In addition, Free Download Manager allows you to adjust traffic usage, organize downloads, control file priorities for torrents, efficiently download large files and resume broken downloads.
FDM can boost all your downloads up to 10 times, process media files of various popular formats, drag&drop URLs right from a web browser as well as simultaneously download multiple files!

[With version 5.0 and newer the source code is not available and the GNU General Public License agreement has been removed from the app.]

VLC is a free and open source cross-platform multimedia player and framework. Owned by the non-profit organization VideoLAN.

Beginner friendly video editor (OpenShot user should change into this)

Experienced user video editor

Full-featured screen recording and live streaming software for Mac, Windows and Linux.

Audacity is free, open source software for recording and editing sounds. You can use Audacity to record live audio, convert tapes and records, edit sound files, change the speed or pitch of a recording and much more.

LMMS is a free cross-platform alternative to commercial programs like FL Studio , which allow you to produce music with your computer. This includes the creation of melodies and beats, the synthesis and mixing of sounds, and arranging of samples. You can have fun with your MIDI-keyboard and much more; all in a user-friendly and modern interface.

GIMP is a free program for such photo retouching, image composition and image authoring. Essentially it's the closest thing to Photoshop you can get for free.

Inkscape is a professional vector graphics editor for Linux, Windows and macOS. It's free and open source.

Krita is a professional Free and open source (FOSS) painting program. It is made by artists that want to see affordable art tools for everyone withith concept art, texture and matte painters, illustrations and comics.

Blender is the free and open-source 3D creation suite. It supports the entirety of the 3D pipeline—modeling, rigging, animation, simulation, rendering, compositing, video editing, and motion tracking.