oscillators designing
EDITS IN BOLD:    

There used to be standard IC that would do this.  ICL8038, XR-205 and XR-2206 might be options.

You can integrate the triangular wave and tune the parabolic wave to be close to a sine wave.  Forum thread, Sine shaper, Circuit ideas, Simple function generator 

You can use deep active filters if your range of frequencies is not too wide and just filter the sine wave.  Nice waveform generator

There are resistor and digital counter DAC pseudo sine wave designs. A patent even

Or these days you could use a PWM digital system to get the signal and use a pulse frequency so high it is easy to filter out the desired fundamental.  This is often implemented as code in a DSP chip or for a simple circuit that does not need any other controller stuff a FPGA type setup like the DIPSY might work.