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Day 2 (On a square grid)
Made completely with

Day 5 (Discovery)
A nebula based on the terdragon , made completely with

Day 6 (Single Line)
There are quite a few made by repeatedly modifying a single line. I decided to go for one of the less well known ones (at least to me), the Fibonacci Word Fractal.
Again, this is made completely in .

Day 9 (Growth)
I appear to have grown some slightly stylised purple fractal mushrooms.

Day 10 (Map)
A Terdragon with adjusted colours and a single added line to get this map-like image.

Day 11 (Proof)
Definitely not a rigorous proof, but maybe somewhat of a demonstration, that this H-curve (at each end of each line draw a perpendicular line scaled down by a factor of √2) fills a rectangular area of the plane.

Day 12 (On an Iso grid)
An isometric Menger Sponge, created in

Day 13 (Zero)
Start with a square, remove the central square with half the side length, then remove squares at each corner with half the side length again, and repeat until zero area remains.
What's left is the T-square (white here).

Day 14 (Irrational)
Start with a line segment. Replace it with two lines at 45° to it, scaled by √2. Keep repeating. You get the Heighway Dragon .
I think the pattern inside is caused by my scaling factor not being exactly √2 ( doesn't allow irrational size)

Emlyn

Day 15 (Triangle)
A variation on the Sierpiński Triangle: split it into 16 ¼-length triangles and remove 3 around the centre. Repeat in each sub-triangle, and you get this.
As usual, made entirely in .

Day 16 (Connected)
The Pentadendrite (a variation of McWorter's Pentigree) looks weird and asymmetrical, but 5 of them connect together perfectly to make this nice order-5 symmetric image.

Day 17 (Symmetry)
Lots of choices for this prompt, but in the end I decided to go for this Vicsek . Even though the colouring actually breaks the some of the symmetry, I think it somehow feels more symmetric than in a single colour.
made in