Quick sketch for a replacement for SelectFont for RF3.

selectFont.py

# coding: utf-8
# replacement for robofab's SelectFont
import os
import vanilla
from mojo.roboFont import CurrentFont, CurrentGlyph, AllFonts, OpenWindow

class SelectFontWindow(object):
    def __init__(self, callback=None):
        self.fonts = {}
        self.callback = callback
        for f in AllFonts():
            if f.path is None: continue
            p = os.path.basename(f.path)
            self.fonts[p] = f
        self.names = list(self.fonts.keys())
        self.names.sort()
        self.w = vanilla.Window((300,200), "Select UFO")
        self.w.l = vanilla.List((0,0,0,-30), self.names, doubleClickCallback=self.callbackSelectFont)
        self.w.open()
    
    def callbackSelectFont(self, sender):
        s = self.w.l.getSelection()
        if len(s)==1:
            selectedFont = self.fonts[self.names[s[0]]]
            if self.callback is not None:
                self.callback(selectedFont)
            self.w.close()

if __name__ == "__main__": 
    def myFunction(selectedUFO):
        print("this is the UFO you selected:", selectedUFO)

    OpenWindow(SelectFontWindow, myFunction)