When comparing Diagrams.net vs Inkscape, the Slant community recommends Diagrams.net for most people. In the question“What are the best flowchart / diagram softwares?” Diagrams.net is ranked 1st while Inkscape is ranked 6th.
Specs
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Pros
Pro Rich functionality for a web-based application
Pro Integrates with multiple cloud storage services
Draw.io offers saving files directly to services such as Google Drive, OneDrive or Dropbox along with saving to to computer.
Pro Real-time collaboration
Pro Great flexibility customizing text labels
Pro Completely free
Pro There is also a Desktop version
Pro Good list of different output formats
Draw.io supports export for PNG, GIF, JPEG, PDF, SVG, HTML, and XML.
Pro Internet Explorer 6-8 and touch device support
Draw.io works with every browser (even IE 6) without plugins.
Pro Free and open source
Inkscape is GPL-licensed and maintains public repositories.
Pro Opens lots of file types
Inkscape supports many common formats for import (including SVG, Photoshop and Illustrator) and its plugin architecture allows more to be added.
Pro Export to different file types
Files can be exported and saved as a "normal" svg, png, jpg, bmp etc. file.
Pro Cross-platform
Pre-built binaries are available for Windows, Mac and Linux. Inkscape can be built from source on additional platforms.
Pro Integrates well into a X11-System
Its uses the X11 icon theme and desktop theme(GTK).
Pro It can do anything
A very powerful software that can do pretty match anything!
Pro Measurement Tool
This tool is extremely handy and can not be found in any other vector graphics programs out there.
Pro Live Path Effects
Extremely powerful menu that offers more than 30 powerful Live Path Effects to apply to paths vastly enhancing the application functionality.
Pro Guides, Grids, and Canvas Rotation
Extremely handy features when building complex graphics using Inkscape.
Pro Dark Theme Support
The new 1.0 beta 2 version finally got support for dark theme which normally is only available for commercial software like Affinity Serif, Adobe Illustrator.
Pro The new version 1.1 is looks and feels fantastic
Inskape got UI update: new dockable dialogs.
Pro Interface is available in 29 languages
Basque, British English, Brazilian, Portuguese, Catalan, Croatian, Czech, Dutch, Finnish, French, German, Greek, Hindi, Hungarian, Icelandic, Indonesian, Italian, Korean, Latvian, Norwegian (Bokmål), Polish, Romanian, Russian, Slovak, Spanish, Swedish, Turkish, Ukrainian, Urdu, Swedish.
Pro It's really easy and fun
Vector graphics can be created and edited with Inkscape.
Cons
Con Import from Visio .vsd is useless
Even simple diagrams get all scattered.
Con Behaves strangely for certain diagram types
For example the snapping function for arrows doesn't work properly for the sequence diagram template.
Con Very slow startup on some systems
Depending on factors like how many fonts you have installed, Inkscape can take upwards of 30 seconds to launch.
Con Uses its own SVG-format by default
Inkscape might use SVG as its default format, however this SVG's contains some additional SodiPodi/Inkscape additions that can be troublesome if you want to import the SVG into some other application.
Con 1.0 is sluggish
Inkscape 1.0 uses GTK 3 which is sluggish and slow for low spec systems( eg. ARM, Celeron, Pentium, Core-i3, Ryzen 3 or Athlon ) compared to previous versions.
Con Buggy
Application is often buggy so it happens from time to time that the popup / right-click menu won't close and stays open. It crashes also sometimes randomly. This makes it almost unusable for productive / business use.
Con Crashes very often
Inkscape encountered an internal error and will close now - is one of its standard messages.
Con Since 0.91 the gradient editor is gone
It is now only possible to edit a gradient on screen. but you can't set a stop to a specific percentage anymore.
Con Limited work with ICC CMYK color scheme
Support for ICC color profiles only in SVG files.
Con Y-axis inverted
0,0 coordinates begin in lower left corner, not upper left corner as SVG standards define in Inkscape 0.92.x.
It seems this is now fixed in the 1.0 beta 2 version of the program.
Con Uses GTK
It looks an feels like an alien. It also uses now touch-based widgets instead of professional widgets.
Con A toy for facebook-ist enthusiasts, not for professionals
It's a Linux niche mumbo-jumbo, same as GIMP for raster edit .
Con Based on the GTK widget toolkit
Software is based on GTK, so it might not integrate well in non-GTK environments. It also requires many dependencies on those non-GTK desktops. It also adds dependencies to GTK-environments since it is written in C++ which requires the gtkmm wrapper/interface.
Con Mac version does not look as polished as its versions for Windows/Linux version for the 0.92.x version
It seems that Inkscape 1.0 beta 2 for Mac got some needed attention and it looks a lot better with dark theme support. native DMG installer and they got rid of X11 which is great.
Con Incompatible with previous versions
Sometimes backward compatibility breaks. For example, pre 0.92 SVGs are incompatible with later releases (due different default resolutions).
Con No support for large printing machine system
No support for large printing machine environment, except exporting the resulting artwork to PDF.
Con Under GNU GPL
It is released under GNU GPL which one of the restricted open source license.