These are simulators for silicon so that wolfSSL can easily regression test for issues with integrations.
The SE050Sim is a simulators for the SE050 which covers basic ECC and RSA functionality.
The ATECC608Sim is a simulator for the Microchip ATECC608A that covers the wolfSSL-required ATCA command subset: P-256 ECDSA, ECDH, SHA-256, RNG, and Config/OTP/Data zone state. It plugs into cryptoauthlib via a custom TCP HAL.
The STSAFEA120Sim is a simulator for the STMicroelectronics STSAFE-A120 that covers the wolfSSL-required STSAFE-A command subset: P-256 ECDSA, ECDH, RNG, and a slot/zone store with a default device certificate. It plugs into ST's open-source STSELib middleware via a custom Linux PAL that pipes the I2C transport over TCP.