Author here: I made Circa because creating circos plots was very difficult and time-consuming when I had to do it during my PhD research. Increasingly people who have genomic data to show are biologists who can't or won't spend days writing code to get a nice circos plot for publication or presentations, so I made a GUI desktop app that helps them do it. I made it extremely flexible so they can style it in every way imaginable, but I tried to keep the UI intuitive and very easy to use.
Circa is a desktop application made with Electron and D3, and it is the first product from my new business OMGenomics, where I also put out free educational bioinformatics content in the form of YouTube videos.