Just about every electronic circuit I designed and built as a teenager used one or more 555's. The most practical was a repeater controller for ham radio. The m

Just about every electronic circuit I designed and built as a teenager used one or more 555's. The most practical was a repeater controller for ham radio. The most interesting was probably a pulse width modulator a/d converter. There was almost nothing you couldn't use a 555 for, and there was almost nothing you should use a 555 for. I remember those circuits not being very stable but then again I am not great at analog circuit design.