Hey HN, I posted Velxio here a while back and got great feedback. Since then I've shipped a major update

What's new in v2:

- 19 boards across 5 CPU architectures (AVR8, Xtensa, RISC-V, ARM Cortex-M0+, ARM Cortex-A53)
- ESP32 emulation via QEMU (lcgamboa fork) — real flash images, ROM function emulation, GPIO/ADC/timers
- ESP32-C3 and CH32V003 run on a custom RISC-V core written in TypeScript, entirely in the browser
- Raspberry Pi 3B via QEMU raspi3b — boots real Pi OS, runs Python
- Realistic sensor simulation: DHT22 (40-bit protocol timing), HC-SR04 (trigger/echo), WS2812B NeoPixel (GRB decoding)
- 48+ electronic components from wokwi-elements

Architecture:

- AVR, RP2040, and RISC-V emulation runs client-side (avr8js, rp2040js, custom TS core)
- ESP32 Xtensa and Pi 3 run on backend QEMU
- Compilation via real arduino-cli
- React + Vite frontend, FastAPI backend
- Self-hostable via Docker, no account needed

Source: https://github.com/davidmonterocrespo24/velxio (AGPLv3)

Happy to discuss the emulation architecture — particularly the trade-offs between in-browser vs. backend QEMU emulation