Interesting question! 👏
I think the first ever OSS project that I made, which was used by a bunch of people, has got to be VinaGUI.
Here's the link for the project.
I built this back in 2014.
Protein-ligand analysis involves finding the interaction affinity between a protein and a ligand molecule. One of the direct applications of this is ligand based drug design, where the efficacies of a database of drugs (ligands) to bind to a particular biological receptor (protein) are tested.
AutoDock Vina is a C program which gives the interaction affinity results for a single protein-ligand pair; I built an automation script which ran the program for a given batch of proteins and ligands; and built a GUI on top of it, to make the whole workflow efficient.