data=Table[Tooltip[OutputResponse[TransferFunctionModel[1/(s^2+2 ζ s+1),s],UnitStep[t],t],ζ],{ζ,{0,0.075,0.15,0.25,0.35,0.5,0.75,1,1.4,2}}];
Plot[data,{t,0,12},PlotRange->All,AxesLabel->{t},Epilog->Inset[TransferFunctionModel[1/(s^2+2 ζ s+1),s],{6.5,1.75}],Frame->True]