Langur is an open-source imperative/functional language written by Anthony Davis. Its principles of design are sensibility to humans, accuracy in calculation, and a clean, expressive syntax.
Influences include the following languages, and likely many others.
I initially developed langur following very useful books by Thorsten Ball (1, 2), but I've made many changes and additions.
I wrote langur to develop skills for another programming project. In the meantime, I wrote a book, explaining how some of langur's advanced features are designed to work in the stack-based virtual machine. See a free preview chapter at opcodebook.com.