Holt's double exponential smoothing, but showing only the trend component.
Even though the Holt's double exponential smoothing is usually used in a sort of an "on-chart average like" indicator with a forecasting part, this version is showing what is not seen in that type of display. The trend component is an integral part of the double exponential smoothing and this version of indicator is showing that part only instead of showing the on-chart value.
As it can be seen, it is useful oscillator and with some experimenting it can work as good as any other oscillator like trend searching indicator.
On the example I left the Holt's double exponential smoothing indicator too for comparison reasons. As you can see, the trend has nothing in common with the slope of the on-chart Holt's double exponential smoothing value. They are not the same and they should not be treated as same. Not even their slopes are the same. For that reason the "trend" version should be used with its own rules (more like a MACD like rules, but without the signal line) then like the on-chart version but it might be a good combination to use the two on the same chart for confirmation of each other (whichever you decide to use as primary). Also the trend version can shed some more light on the forecast part of the on-chart version.
This version has alerts too - they are triggered on zero line cross.