Smish
Smish
Smish is an activation function defined as $f(x)=x\cdot \text{tanh}(\ln(1+\sigma(x)))$ where $\sigma(x)$ denotes the sigmoid function. A parameterized version was also described in the form $f(x)=\alpha x\cdot \text{tanh}(\ln(1+\sigma(\beta x)))$.

Paper: Smish: A Novel Activation Function for Deep Learning Methods

Source: https://www.mdpi.com/2079-9292/11/4/540