Whisk

Back in my day, we didn't have no fancy Blenders to make our models. We placed each vertex by hand, and we liked it that way! - Grandma, probably

Whisk is a simple 3D modeling application that lets you place each vertex, and build simple geometry. I provided a web app to try out the program, but I would advise downloading if you want to spend more than a couple of minutes with the application.

Whisk'in is easy! You should be able to get the hang of it in 15 minutes or less. Just place your vertex on a plane, then connect it to two more to get a triangle. Whisk exports to .obj, .tscn, or .gltf, so you can use your models anywhere.

By the way, if you don't like using a mouse, you can try whisk'in with a controller. Just press the right trigger to bring up a shortcut cheat sheet.
(Tip: hover over a button to see the keyboard shortcut)

This tool is open-source, so feel free to check it out, or contribute here: https://gitlab.com/sdggames/whisk 

Payments are active, but please try it and love it first :)