This is "Ded", a diagram editor intended to be used to make boxes-and-arrows diagrams of the sort common when documenting software systems.
The core is boxes and arrows.
Boxes, which can represent entities in an entity-relationship diagram, have a name and optionally some "attributes", additional text below the name. Boxes have a few shapes to choose from.
Arrows, which can represent relations, usually go between boxes. When a relation endpoint is connected to a box, it moves with the box. Relation endpoints can just float in space however. By default, relations are drawn as straight line segments. Control points can be added to route them more precisely. They are not "smart", but it is fairly easy to route them aesthetically.
There are also inheritances, intended to represent specialization. The main arrow always points at a "parent" entity (superclass). Then, other entities (subclasses) can be associated with it via relations.
I draw a lot of software diagrams. This editor is intended to be efficient for a proficient user to use a combination of mouse and keyboard to accomplish most tasks. Menus are provided primarily as a learning aid.
Most operations snap to 5 pixels unless Shift is held. 5 pixels is big enough that it's pretty easy to eyeball alignment, yet small enough to allow fairly tightly packed diagrams when needed.
In dialogs, take note of the mnemonic letters on the labels. When you see a label with an underlined letter, press Alt+ to jump to the associated control. Tabbing also works of course. The dropdowns also respond to keystrokes; type the first letter(s) of an item to choose it.
Relatedly, every time the file is saved, it is exported as PNG. That only takes a moment (~200ms) and ensures you don't have to think about explicit export. Just save the file.
Ded uses Java and Swing for maximum portability. All you need is the JAR file and a JRE.
I know Swing is not great. It is better than 10 years ago, but that is not saying much. Fortunately, I don't need much from it, and you can't beat its portability.
Right now, the JAR file is only ~300 kB. I won't promise to keep it that small forever, but small size is important to me, so bloat will have to be justified. I won't pull in big libraries without good reason.
A given .ded file will appear the same on any machine, any OS, pixel for pixel. It exports to the same PNG, byte for byte. This is really important when you have a large development organization on lots of platforms collaborating with diagrams. The predecessor to Ded had problems in this area; see comparison-to-ered.txt.
As the tool evolves, the file format grows. But it is versioned, and the deserialization code designed to read all old formats. It can and will continue to read all of the JSON formats that have existed, and all of the predecessor's binary formats. I don't change the format without ensuring the ability to read the previous format.
I store all my diagrams in revision control along with their PNGs. The diagram JSON format is intended to be amenable to a certain amount of automatic conflict resolution, and when that doesn't work, you can at least eyeball the diff to see what changes the other person made. The PNG being always the same means that just exporting again isn't going to introduce a spurious change.
The editor can semi-automatically create entities and relations that depict elements of an arbitrary graph structure. See Using ded to make diagrams of graphs.
The source code is fairly well organized and well commented. You should be able to dive in and start hacking.
There are automated tests for serialization and deserialization. (No automated UI tests though right now.)
This diagram shows most of the diagram features:
This list of other diagramming tools is far from exhausitve, of course; they're just what else I've tried. The short version of all of these is I want something simple, fast, and convenient to use within a software development workflow, and other tools did not meet all my requirements.
Microsoft Visio is a general-purpose diagramming tool, and at its core shares a similar idea of having boxes (and other shapes) connected by arrows that automatically follow their source and target entity.
However, Visio's many capabilities diminish its effectiveness for simple diagrams; it takes more interaction effort to create a comparable diagram for cases like the one above.
It is only available on Windows, and its files do not interoperate well with revision control systems.
All of the the above also applies to PowerPoint and Word when used as diagram editors.
Xfig has somewhat better portability, although still often a hassle to run on modern systems, and acceptable revision control interaction. It falls short on UI efficiency, and the UI is extremely unconventional, making it harder for others to collaborate.
Balsamiq is a dedicated UI wireframing tool. DED has rudimentary features for UI wireframing. See comparison-to-balsamiq.txt for more details.
Only of historical interest; see comparison-to-ered.txt.
To build it from the command line, run make. The Makefile uses
GNU make syntax.
It will also build in Eclipse using the supplied project files. There's nothing special in them though so you can disregard them and use whatever IDE.
The only build dependency is the JDK. It probably needs Java 1.5 or later; I'm using 1.6 right now.
After building it, run the ded script, which does, in essence:
$ java -jar dist/ded.jar
Once it is running, Help|Help explains what to do.
BSD license. See license.txt.