Scikit-learn. The guys have done, and are continuing to do, an amazing job and the output is completely free. There is some funding involved, but the ultimate value/cost ratio is ridiculously high.
I remember downloading VLC for the first time and being overjoyed with the ease, reliability and compatibility. Nothing has changed in the years since then, something most software can't say.
TreeProjects Personal Database: http://personaldatabase.org/ - searchable, inter-linkable, hierarchical notes and media tracking for projects
Godot Game Engine: https://godotengine.org/ - the scene graph system wherein a "scene" is just a saved subtree of nodes and can be instantiated at any point within a parent scene is so far beyond the clumsy scene/prefab split in eg. Unity
Interestingly, Blender was originally proprietary, and was open-sourced after its parent company went bankrupt, and only after money was raised from the open-source crowd (before crowdfunding was a thing).
Also all of python (absolutely beautiful language) and the associated eco system. I’m thinking mostly of numpy/scipy/matplot lib etc, but there are so many more.
It was said in jest, but emacs really is amazingly good for what it costs. Even more so if I consider each of the individual contributions that I take advantage of from so many other contributors. Helm, org-mode, use-package, paredit-everywhere, ace-isearch, magit, undo-tree, ...
The list really is quite impressive. And then there are the things I don't use, but still impress the hell out of me. Skewer mode being the frontrunner there.
Then there is Firefox. Easy to complain about memory usage and whatnot, but it really is an impressive piece of engineering for what I paid for it.
KDE Plasma for me, it's amazing how good it is and how stable it has become. I've been using KDE for years and I've recommended it to almost anyone I could - and they always stuck with it, because it was simply too much well done. Compared to gnome 3 and other new desktop environments, KDE has always been so easy to use, predictable and customisable, a very joy to use.
Any number of programming languages and their implementations. My personal favorites being Nim, Lua, and the sadly forgotten Tcl/Tk.
Linux. Arch for my fancy stuff, Alpine for my servers.
SQLite and Fossil, from the inimitable D. Richard Hipp, plus rsync and rclone to keep everything in its place.
Yes, I'm a minimalist.
Of course, good is so intrinsically tied up with free that we cannot pry them apart. Not for the sake of money (I do contribute, I do donate), but for the convenience and accessability, and of course the principle.
How would you compare it to Photoshop and what would you say to a Photoshop digital painter to get them to switch to Krita (or at least try it out for a while)?
Zim Desktop Wiki (http://zim-wiki.org/). It is great note taking application that supports Rich Text features such as bold, italic, checkbox and bullet lists. It also supports Greek letters, subscripts, superscripts, and Unicode, making it very useful for entering mathematical equations.
I'm still in awe that no matter what coding stack you use, you can almost always do everything you need without paying a dime.
With Microsoft, even Visual Studio Team Services is free - private Git hosting for up to five users, a decent CI/CD orchestration platform, a private Nuget feed, project planning, etc.
not sure if this counts, but as long as you have a .edu account, all of JetBrains stuff is technically free. i've been using all their IDEs since school, and continue to renew my licenses with my .edu email no issues.
Thanks for mentioning draw.io. After a quick look around I can see that it will be very useful. I especially like the interface. If it wasn't for my browser interface above I would swear this is a very well made desktop app. Standard OS inputs used well are hard to beat. This really makes me think twice about using some of the fancy UI libraries out there.
Well, if you want something for editing photos that is truly free as in beer and speech, try the awesome darktable: https://www.darktable.org/
I'm also always blown away by how incredibly easy to use and at the same time how powerful hugin is. In this long list of for-pay stitching applications, Hugin is the only one of two which are free (again, beer and speech) https://en.wikipedia.org/wiki/Comparison_of_photo_stitching_...
Cygwin. Yea, it's mostly just a collection of other free tools, but most of us in corporate America still find ourselves using Windows, and Cygwin is the only thing that makes the Windows command prompt bearable.
On a related note I have been wondering why artist's never provide quality content for free. You know graphics/images for games etc and music/sound effects for example.
Coders provide software worth billions in man hours for free and trying to find quality "artistic" content is impossible. Every little clip art image costs many dollars.
Why do coders provide their services for free so generously while artists are mainly worried about their copyrights?
Not true in that absolute: There is tons of freely licensed music out there. You can find free game assets for genres that are somewhat "generic". But still it is a thing, a few theories on contributing factors:
a) More typically an individual work, with one person having a vision that they do not want to have compromised by others. Arguably harder to have contributions in a way that doesn't stand out in many cases, which means one work made by a small army of contributors sharing the workload doesn't happen often.
b) the "work for me for free" demands are worse for artists than for coders. "Freeloading" is seen a lot more critically/abusive than in software circles. (although it does happen with open-source projects as well of course, and long-term maintainers burn out accordingly as well).
c) approximately nobody pays artists to produce freely licensed works
d) free work by artists might be in direct competition to their ability to make money from their art.
e) Parts vs final product: a lot of open-source development is in pieces that other projects build on. Similarly, you can find quite a lot of "pieces" of art for free: sound templates, stock/reference images, textures, ..., which is not very visible to someone looking for "free graphics". Similarly to how many people not involved with software do not understand on what mountain of free libraries a lot of software stands.
f) More visible if reused, which leads users of graphic resources to want individual ones instead of the same as everyone else. E.g. games will more likely stand out by graphics but use the same engine as X other games.
New Relic. Unfortunately it reduced their free plan (and the paid plan is expensive), but I was always amazed about their free features. I'm still didn't find a good alternative. :(
"How Open Source is Really Maintained" comes to mind: https://cdn-images-1.medium.com/max/1280/1*Q_8HbGbbfEmAjwPqB...