I propose to copy all these images in one Google+ photo album, and make people vote for their best choice

I couldn't resist! Cool thread!
3D Random objects, cubism, ink-wash, edges, plasma, canvas texture, relief-light, sharpen, frame, dropshadow.

I love that Chris, sure nice to see you back.

Here is my third attempt, more 3d-ish than before :

Good idea David

Is there any limit for image contribution per user or a time limit when this submission ends?

And is text allowed? With the watermark module text can be generated and with different fonts like webdings, this could be considered cheating?

inglorious : no, there are no time limit, it is just for fun (and nothing to win too ).
So please post multiple attempts if you wish.

Text could be added, but I guess only with the use of G'MIC (so very few possibilities to do it, like 'Quick copyright' or 'Visible watermark').
The fun is to use only G'MIC, if other filters or tools from GIMP are used, this could be not a part of this challenge.

Ronounours, about the idea "To make people vote for their best choice", I disagree with you. There is already sufficient competition in whole world. We should have avoided that this competition reaches us also. I suppose that the praises that appear spontaneously in the GC are already a sufficient stimulus for our creative artists.

Carlos, when I say 'vote', I just want to say that they can +1 the pictures they prefer (eventually, they can vote for multiple entries).
I don't want to make a ranking or something like this, this challenge is just for fun, nothing else.

Here is my entry . Started off with 4 tiles, then forgot , then window glass and adjusted something in colours. Gmic only

nice wooble, it would make nice wallpaper

Sorry, Ronounours. The difference in cultures produces these misunderstandings.
I had understood that the goal was to establish a ranking.

Started with black
Array - Random Colors
Array - Mirrored
Deformations - Perspective

On a duplicate layer, Deformations - Circle Transform, Contours - Difference of Gaussians, then blend with the original layer using Layers - Blend (Standard) Lightness

Then my notes get hazy ?

Then Artistic - Cartoon, Textured Glass and Psychedelic Glasswork. What fun!

I was over-thinking. This time a simpler workflow: 4 steps.
White base layer
Array - Random Colors
Artistic - Psychedelic Glasswork (white separators)
Artistic - Watercolor

Another little one, to keep practising

[G'MIC] Denim texture : -Denim_samj 5,2,0,40,40,25,50,0,43,108,126,255,255,255,255,255,0,0
[G'MIC] Random color ellipses : -gimp_color_ellipses 400,8,0.1
[G'MIC] Tetris : -gimp_tetris 10

I had to have another go, but I have no idea what has been created. Maybe it's a green version of that old sci-fi series The Time Tunnel. Just need a couple of guys rolling around inside it now.

Wow. G'orgeous and G'fun. And worth doing just to find out what will happen if....

I had each step create a new layer, and took screenshots, and still forgot to document one step, but I remembered what I did and noted it after. Should have had the screenshot, though, for the settings. Anyhowl, here is a hippie doodle. Details in short are:
Mandelbrot
Mosaic
Plasma (merged w/Mosaic)
Stained Glass
Relief Light

It's hard to know when to quit. And it's hard to quit!
Smooth [thin brush]
Local normalization