I’m retired programmer. I did most of my work in C. Did some C++. And Ruby is my favorite language. I did Macintosh development back in 1985 when the first Mac came out and have not done much UI coding since. I did mostly device drivers. I did a lot of Ruby on Rails work from 2007 to 2015. I am considering writing a spreadsheet app. Some items I would like to implement is the ability for what is displayed to be more complex than what Numbers (for example) allows. I would also like to implement the concept of Units like the old HP calculators did. Ultimately I would like users to be able to create functions easily. If possible, I’m leaning towards using Ruby as the language that these functions could be written in but that is just an example. It would be best to assume I’ve not done any macOS development since what little I have done is centuries old. What language would you suggest I use? Are there perhaps a few skeleton applications that I could start from? My main bewilderment is how to create a window, put elements in it, make the elements interactive, etc.