Inkscape is an open source software for vector graphics edition. Inkscape is oriented for professional use, therefore it is required some training with it, but the results obtained have an excellent quality. There are also many tutorials in both formats, text and video, which can help us to get starting with this software.
Inkscape can be downloaded form the official page, or in the case of Ubuntu systems, it can also be installed via terminal.
In Chemical Engineering they can be used to create nice figures and diagrams with professional quality to be used in publications or presentations, facilitating the understanding of the subject being dealt with. An example of a diagram made with Inkscape can be found below.