\[ y''(x)=\frac {y(x)}{e^x+1} \] ✓ Mathematica : cpu = 0.281602 (sec), leaf count = 42
\[\left \{\left \{y(x)\to c_1 \left (e^{-x}+1\right )+c_2 e^{-x} \left (e^x \log \left (e^x+1\right )+\log \left (e^x+1\right )+1\right )\right \}\right \}\] ✓ Maple : cpu = 0.049 (sec), leaf count = 27
\[ \left \{ y \left ( x \right ) ={\frac {{\it \_C1}\, \left ( {{\rm e}^{x}}+1 \right ) \ln \left ( {{\rm e}^{x}}+1 \right ) +{\it \_C2}\,{{\rm e}^{x}}+{\it \_C1}+{\it \_C2}}{{{\rm e}^{x}}}} \right \} \]