Glyphs"is a Mac font editor that puts you in control: quickly draw high-precision vectors, efficiently reuse shapes, and easily manage any number of letters, figures and symbols." The editor is used by Rasmus Andersson for the creation of Inter, but it catched my attention while reading the
interesting article A font for the people by Olivia King. Olivia is explaining the process of picking up an open-source font and modifying it for specific use. I got pointed to it by Mark Boulton who had in his typespecimens newsletter.