Insiders explain how fractional-share trading went from fringe to must-have — and who's actually doing it in an industry where everyone wants to be an early mover

· The rise of self-directed fractional-share trading is a product of the fiercely competitive, margin-pressured environment that startup and legacy brokerages alike are operating in today.
· Players like Robinhood, Fidelity, and Charles Schwab have raced to announce their own offerings — marketed largely at customers still...