\[ \boxed { {\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left ( x \right ) +a \left ( {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) \right ) \left | {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) \right | +b\sin \left ( y \left ( x \right ) \right ) =0} \]
Mathematica: cpu = 41.170228 (sec), leaf count = 27 \[ \text {DSolve}\left [a y'(x) \left | y'(x)\right | +b \sin (y(x))+y''(x)=0,y(x),x\right ] \]
Maple: cpu = 2.246 (sec), leaf count = 56 \[ \left \{ y \left ( x \right ) ={\it ODESolStruc} \left ( {\it \_a},[ \left \{ \left ( {\frac {\rm d}{{\rm d}{\it \_a}}}{\it \_b} \left ( { \it \_a} \right ) \right ) {\it \_b} \left ( {\it \_a} \right ) +a{\it \_b} \left ( {\it \_a} \right ) \left | {\it \_b} \left ( {\it \_a} \right ) \right | +b\sin \left ( {\it \_a} \right ) =0 \right \} , \left \{ {\it \_a}=y \left ( x \right ) ,{\it \_b} \left ( {\it \_a} \right ) ={\frac {\rm d}{{\rm d}x}}y \left ( x \right ) \right \} , \left \{ x=\int \! \left ( {\it \_b} \left ( {\it \_a} \right ) \right ) ^{-1}\,{\rm d}{\it \_a}+{\it \_C1},y \left ( x \right ) ={\it \_a} \right \} ] \right ) \right \} \]