Wokwi is an online Electronics simulator. You can use it to simulate Arduino, ESP32, STM32, and many other popular boards, parts and sensors.
Multisim Live is a free, online circuit simulator that includes SPICE software, which lets you create, learn and share circuits and electronics online.
Tinkercad is a free, user-friendly, web-based 3D design, electronics, and coding tool. It's known for being a great introduction to Autodesk, particularly for beginners.
Fritzing is an open-source hardware initiative that makes electronics accessible as a creative material for anyone.