Developer Max Woolf released `ballin`, a Rust-based terminal app that simulates thousands of balls with realistic physics. Built on the rapier 2D physics engine, it achieves 120+ FPS with 10,000 balls using Braille Unicode for visualization. The tool supports interactive features like geysers, shape obstacles, and gravity adjustments, all within a command-line interface.

The project demonstrates how terminal UIs can handle complex simulations without a graphical stack. Woolf used Claude Opus 4.5 to initially prototype the Braille visualization concept, which he then expanded into a full interactive experience. The app intentionally avoids the latest rapier version due to stability issues, opting for version 0.31.0 for reliable performance.

`ballin` includes exportable JSON levels and CLI arguments for customization. It's designed for high-performance terminals like Ghostty, as native terminals like macOS Terminal.app may cap frame rates. The project highlights the growing capability of Rust for real-time graphics and physics in constrained environments, offering a playful tool for exploring terminal-based simulations.