RedArrow has never been properly ported to RoboFont 4, and interest in it seemed low. Check out Glyph Nanny (which is much more exhaustive than RedArrow ever was) if you are looking for outline drawing critique.
RedArrow for Glyphs is still actively maintained.
Finally you can have red arrows in RoboFont too.
When the extension is active, red arrows will point to possible mistakes in your outlines.
These kinds of errors are detected:
- Missing extremum points
- Fractional coordinates
- Fractional transformations
- Incorrect smooth connections
- Empty segments
- Collinear vectors
- Semi-horizontal and semi-vertical lines
- Segments on "closepath"
- Zero handles