Diagram, flowchart, and graph
Flowchart is most frequently used as I am a programmer (though not as my career). If using Microsoft Office, it provides drawing tool for preparing flowchart. It is easily to be used. Since my primary office suite is LibreOffice, I frankly admit that drawing tool in LibreOffice is not satisfying to complete my work. This is because, preparing the graph or diagram, using a paper layout is not convenient, because I have to make sure that my flowchart is within the paper.
The next thing is the keyboard/mouse control differences. I get used to the way of controlling the image editor such as GIMP and Inkscape, that is, dragging the view with the middle mouse button, zooming by scrolling the scroll wheel together with Ctrl key, and right-click for the context menu. However, in LibreOffice, zooming can work with the Ctrl+Scroll wheel, but not dragging the view. This causes the trouble. Therefore, I have looked for the alternative solutions.
Dia
Dia is my primary flowchart editor. It can be used to draw the maps, CISCO network, UML, etc. However, the problem is the integration with the LibreOffice. The best solution is to export the diagram to the raster image (such as PNG), then insert the image in LibreOffice. It is preferable to export as vector image such as SVG. However, I previously experienced the problem of rendering SVG in LibreOffice, thus I seldom export as the SVG format.
Some of the drawback in Dia is text editing. When editing text item, the text cannot be highlighted or copied. It causes the difficulty to edit the text.
Calligra Flow
Calligra Flow can save the file as ODG format, which is also the same format as LibreOffice Draw. However, they are not perfectly compatible. The advantages of Calligra Flow comparing to LibreOffice Draw, Calligra Flow provides the flowchart elements, UML elements, and other elements just like Dia. Yet, input control for Calligra Flow is also different from GIMP or Inkscape. Thus, I still prefer Dia rather than Calligra Flow.
yEd
Recently I have to prepare the (mathematical) graph. Dia has difficulty for me to prepare the graph. There is a solution by using the Graphviz. Yet Graphviz does not allow me to adjust the graph easily. Finally, I discovered yEd. Using yEd to preparing graph is very easy and intuitive. Though, dragging the view is using right-click instead of middle-click.
Other that preparing the graph, yEd also allows to prepare the flowchart. The graph can also be exported as SVG format.
Though it does not provide various diagram elements like Calligra Flow or Dia, it allows to draw the mathematical graph and it has the feature to snap and arrange the diagram elements in very neat order.
As a conclusion, these are 3 diagram drawing tools other than LibreOffice Draw. When we are going to prepare the mathematical graph, yEd is recommended.