Today I made a pattern called metaballs (I believe that’s the name :)), with three variants:
Click here to download. If your graphics program accepts pat files, just install these files in the appropriate folder (usually this is the “patterns” folder). If you use Gimp, Krita or Photoshop, see this video, starting at 12:14, for more details.
Here is an example usage, in Krita. I applied each variant on separate layers, set to Grain Merge mode, with 60% opacity, above the green background:
