Is there a stylus for non-iPad Pro models?
The Apple Pencil only works on iPad Pro models, but plenty of third-party stylus work on older iPads. A lot of stylus are "dumb stylus" that don't offer advance features, but one model, the SonarPen, uses the iPad headphone jack to offer a battery-less and pressure sensitive stylus. The SonarPen also offers palm rejection and promises to perform "like its more expensive competitors on the market."
The Hong Kong-based company Greenbulb has raised over $45,000 on Kickstarter to manufacture the SonarPen. It will be available around June 2018.