Depending on what your focus is you could go a few different ways for an upgrade. I'm going to focus on open-source but talk about free alternatives. So I see three main ways you could go for an upgrade you might consider taking all three so you can gravitate to what works best for the task at hand. If you are strongly in the charts but still want some art tools you might consider libreoffice. It is basically Microsoft office but open source. One of the programs is Draw. It has tools to make many traditional diagrams like decisions trees and mind maps easier. It is also going to be a little bit more friendly with . Google has a similar drawing package Drawing but I find it too simple. I am used toplex software packages so that could just be my bias. Paint .net is generally excepted step up from paint on window. The big problem is that it is only ok for personal use so I don't rmend it. Pinta is great alternative as is kolourpaint or luxpaint. All these similar but the feature that will really help you is layers. It will speed up layout by not always drawing of what you just drew. Aside that the major advantage here is these programs are basically light versions of Gimp and they are most similar to paint and how you have done things in the past. Inkscape is the middle ground option. It is a scalable vector program so the brushstrokes and objects you draw will be discreet objects that can be edited after the fact. Things like the shape color line and weight are not set in stone after you draw that line. They are all repositionable so they are have the abilities of layers. It does what it does well but can be somewhat to a somewhat illustrated or cellshaded style. This would work well for diagrams and give a lot of freedom anything else you want to do. This bit here might not be of too much use. Looking at these option this is how I see it. I would be a bit concerned about being limited by Libre Draw but I think it would be effective at doing what it can do. My experience has been I hit little things I can really do or the features get in the way of doing what I need to do. It's been the same any similar version. Using something like Pinta doesn't feel precise but can feel quick. This is very subjective. I can be accurate to the pixel but it doesn't generally allow the same amount of tweaking and fine tune of shapes as Inkscape. They are both very different approaches. Re Gimp So Gimp is basically the next step beyond Pinta andpany. Gimp does add a lot of photo editing elements but also has a much stronger layer system a much more evolved brush system better selection tools some vector based tools tablet support and the list goes on. This makes it a very versatile piece of software but other software does individual elements better. The vector tools in Inkscape are way better than Gimp particularly because the vector tools have so many roles to play in gimp. I don't really use pinta or that kind of software often because Gimp replaces it nicely but I do use Inkscape.