Velxio is an open-source, self-hostable simulator that runs Arduino, ESP32, and Raspberry Pi boards entirely in a web browser — drag and drop a board, wire up components, write Arduino C++ or Python, compile it, and watch it run with a working serial console, all without touching physical hardware. It supports 19 real boards, including the Arduino Uno, ESP32, ESP32-C3, Raspberry Pi Pico, and Raspberry Pi 3, alongside 48-plus interactive electronic components.
Real emulation, not an approximation
The distinguishing technical claim is that Velxio runs real CPU emulation rather than simulating the behavior of a sketch at a higher level — meaning code compiled for an ESP32 actually executes against an emulated ESP32, timing quirks and all. On the analog side, it goes further than most browser simulators bother to: ngspice, the long-established open-source SPICE circuit simulator, is compiled to WebAssembly and runs real-time analog simulation with non-linear devices — diodes, BJTs, MOSFETs, op-amps — rather than treating every component as an idealized digital black box.
Multiple heterogeneous boards in one circuit
A capability worth calling out for anyone prototyping a multi-device installation: Velxio supports multiple heterogeneous boards in the same simulated circuit — two Arduinos talking over SPI or serial, an ESP32 paired with an Arduino, a Raspberry Pi 3 talking to a Pico. That’s exactly the topology real interactive-art and installation projects tend to take, and it’s the configuration that’s hardest to test on a bench without buying every board in the chain first.
Self-hosted, dual-licensed, no cloud dependency
The self-hosting story is the other differentiator. Velxio can run entirely on your own infrastructure with no cloud dependency, which matters for classrooms, workshops, and anyone unwilling to make their prototyping workflow contingent on a hosted service’s uptime or pricing. It’s dual-licensed — AGPLv3 for personal, educational, and open-source use, with a commercial license required for proprietary or SaaS products — and there’s a hosted demo at velxio.dev for anyone who wants to try it before standing up their own instance.