Illustrator space fill plugin can be found in Astute Graphics' ColliderScribe set. It is a super powerful tool for filling paths with other paths. To use it, simply select a large path (the fill) and select a smaller path or paths and then use the associated and named panel.
Create a path such as rectangle (this is the path to be filled) as a container for the 'space fill' plugin. Create a path or multiple paths and these are the paths that are used to cover the first path. Select all of them. Go to the window menu and ColliderScribe and select the panel.
Set the various settings and then click "make".
It works with all kinds of paths such as type and also normal paths. It can be packed with different colorful paths. You can also use type with paths and paths with type and all kinds of other combinations. You can stuff the paths with all kinds of stroked open lines and curved paths to create amazing sketch artworks, grid designs, line artworks and more.
It is a live effect so it can be edited and modified in many ways via the appearance panel.
The tool includes many different settings as well as randomization features such as scale and rotation and opacity
You can expand and release items - the release generates a lot of groups so if you don't want the groups, just go to the object menu and use the ungroup a few times and you can see the results of that in the layers panel. You can then manipulate the individual paths such as move them or re-size etc
You can use it with the color guide to create endless colorful designs, of course, you can also use it with the powerful Randomino tool from Astute Graphics
The key thing is that the main path is 'bigger' than the objects
You can select the container and also select multiple other paths and then apply the effect. The result will be multiple copies of each of the individual paths but the result will be the design spread out across the container. If you want the design as is then you will need to select and group all the paths together via the object menu and group command and then you will see the container filled with all the designs as displayed.
You can select a large circle (or any other shape) as the container and then create another shape such as another circle, change the color perhaps. Apply the effect and set the copies to 200 as well as resize and vary size (perhaps go for 2 etc for that) and click randomize. Once you are happy with your design, expand via the top button. Go to the Randomino and then select the design and also click the ignore grouping (or just ungroup multiple times) and then set the range for the random dot colors and click randomize and stuff your art with blues, greens and reds. Youtube video on subject