I came across an article on 3ders.org several weeks ago and wanted to share it here. It's about a web browser-based, online 3D design (CAD) tool called PlastiSketch: http://www.3ders.org/articles/20180319-plastisketch-browser-based-software-uses-vector-graphics-to-design-3d-models.html.
I know that 3D printing interests a lot of model railroaders. However, the learning curve for 3D design or CAD tools has scared a lot of them off from designing their your own objects. They are also expensive and with many model railroaders engaging in the hobby part time, this can also be a barrier. That's why I'm always on the lookout for new tools that may be able remove or at least lower these roadblocks.
PlastiSketch is very unique because it doesn't start you out using a 3D sculpting approach. It starts out from a 2D perspective and then allows you to add layers on top of that, gradually building a 3D object. All you need to be able to do is be able to draw out the flat shape and then you can transform it to a 3 dimensional shape using PlastiSketch.
It's also free to use and it's all online, so all you need is a modern web browser and a decent internet connection.
I've only used it a little bit and plan to do more in the future. I think it could be a decent tool once you get the hang of it. Here's a direct link to PlastiSketch.