Best Free CAD Program
Sweet Home 3D is sure to tickle every bone in your body. You can model your dream home, along with all of its cherished appointments, and then watch it come to life. You can start simple with just the bare walls or import an image of your intended floor plan to serve as a basis for the design-to-be.
The user interface is as intuitive as it gets; drag and drop furnishings from the built-in catalog onto your floor plan. Clear graphic handles then make it easy to edit the items. Once you've finished your home design and tweaked every niche and corner to your liking, the fun has only just begun. (Review)
Blender , a complete software package for 3D modeling, texturing, rendering, animation and physics. It has a complex but merciful user interface, and the entire repertoire of its capabilities are made available through a scripting language, so the creation of 3D games beckons.
The software can import from and export to more than 20 different file formats. There is a large and growing community of Blender users who've already contributed numerous add-on scripts that can make your going easier. If it can be imagined then it can be realized, with Blender freeware. (Review)
Best Free High Dynamic Range (HDR) Software
Luminance HDR (previously known as Qtpfsgui) is an open source graphical user interface program and a high quality application to provide a workflow for high dynamic range imaging.
It has great tone-mapping and aligning facilities, allowing for 8, 16 and 32 bit channels and two means of manually manipulating the image.
Best Free Image Editor
GIMP , currently the only freeware package I am aware of that can be called an advanced image editor.
If you are inexperienced at using image editing programs GIMP will likely be too overwhelming to start learning on as it has a steeper learning curve but it is feature rich. It has lots of advanced features and can do almost everything the Photoshop can do.
Its multi-windowed interface makes it a little unusual if you're used to a windows program. (Review)
Pinta , a simplified alternative to GIMP and modelled after the popular Windows program Paint.Net, Pinta is good for average users and includes most basic features including common drawing tools, resizing and cropping, adjustments and effects for tweaking images as well as supports for multiple layers.
Best Free Image Optimizer
Trimage makes your image files smaller and more suitable for use on websites, sharing on social media or sending by email. It supports PNG and JPG formats, shows compression levels and optimizes multiple images in one go, using optipng, advpng, pngcrush and jpegoptim.
Best Free Image Stitcher
Hugin , a GUI front-end of Panorama Tools allows you to stitch overlapping digital photos taken from the same location into a complete panorama, with advanced features and workflow options such as correction of exposure and white balance, generate HDR, supporting a full range of cameras and lenses, multiple rows of photos, cropping, masking, control points, optimizer and more.
Best Free Image Viewer
XnViewMP , a multi-platform and enhanced version of XnView, is a media or graphic browser and viewer available both in 32 and 64 bit versions, with speed-optimized loading, improved caching and multi-core processing. It also has a powerful batch image converter built-in.
Provided free for private and educational use, this app supports more than 500 formats in reading and export to about 70 different file formats.
Best Free Paint Program
MyPaint , designed for pressure sensitive graphics tablets, MyPaint allows you to use a large collection of brushes including charcoal and ink to emulate real media, with color changers and opacity controls, unlimited canvas and basic layer support.
You can also download and import more brush packages for use with the application.
Krita , a user-friendly and feature-rich sketching and painting application for raster images, complete with real-world painting materials and workflows, multiple brush engines, blending and wrap-around modes, advanced selection and masking tools, symmetry tools, drawing aids, filters, effects, layer and color management.
Best Free Photo Organizer
digiKam , a digital photo management program designed to import, organize, enhance, search and export image files. With this you can add comments and tags to albums, view and edit items, create slideshows and calendars, and share your creations.
Phototonic , an image viewer and organizer to load thumbnails and browse images on a folder tree. Some key features include image navigation, file management, slideshow, transformation, adjustment, display image info and metadata, rotate images based on the Exif orientation tag, find and manage duplicate images, etc.
No executable package is readily available but general instructions to compile the program code and create the executable are given on the developer's homepage.
Best Free QR Code Generator and Decoder
QtQR , a graphical frond-end for python-qrtools allows you to easily create and decode QR codes, supporting URL and other data type, configurable pixel and margin sizes, error correction, and save QR Codes in png format.
You can also use it to decode a QR image from a file on your computer or captured on a Webcam. (Note: Install python-qrtools in your system before installing QtQR; both debian and rpm packages are available.)
Best Free Vector Graphics Editor
Inkscape , a top product enhanced by an excellent user interface and the impressive set of tutorials, helps wean the user away from the world of digital images to the nodes, lines, curves and shapes that form the basis of vector editing. (Review)