Yes, there is other signals broadcasted by aircraft, although not by all. In the General Aviation sector, at least in Europe, an on-board device known as FLARM is being used mostly in Gliders, Helicopters, Single-Engine Piston aircraft and touring motor gliders.
FLARM is an electronic device to selectively alert pilots to potential collisions between aircraft. It is not formally an implementation of ADS-B, as it is optimised for the specific needs of small aircraft such as gliders, not for long-range communication or ATC interaction.
You can visualize these signals using some tools and you can also feed the data to sites like flightradar.
Related Answers to FLARM:
What system is there in the UK to prevent collisions between small aircraft?
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