We are working on some projects about dynamical analysis of two dimensional oscillators described by differential equations. We appreciate if you can introduce us the interesting cases you have dealt with. E.g. we know that Van der Pol oscillator is a famous well-investigated example of such systems. Or Shi-Songling system is an important example related to “Hilbert's 16th problem for quadratic vector fields”. Multi stable oscillators are very interesting for us and we would be glad to know important cases from this category.