[TheAceOfHearts]

I don't know about electric cars, but for gas powered cars there are open source ECUs [0][1]. There are also tuners that directly modify the car's firmware to improve performance. Finally, you can connect a computer to the CAN bus [2], which allows you to capture and replay commands, as well as craft your own commands. This is how Comma's openpilot [3] works: it connects to the CAN bus and sends commands for all supported functionality.

What kind of features did you have in mind?

[0] https://en.wikipedia.org/wiki/Engine_control_unit

[1] https://rusefi.com/

[2] https://en.wikipedia.org/wiki/CAN_bus

[3] https://comma.ai/openpilot

[whaleofatw2022]

There's also the Megasquirt for fuel timing, which is not quite open but not fully closed off either...

[gia_ferrari]

For full open source, there's Speeduino and FOME (newer). I've used both for my cars. https://speeduino.com/home/ https://wiki.fome.tech/