This might be kind of a trick since I've used this alternative exchange system for years now... but I just think it`s important to share and those years have helped me to know this exchange system actually works!!!!
This can be called a "local" karma system but basically the systems works this way:
Help everyone so you'll get help when you need it!!!
I think the system needs no further explanation, but I'll put an example. I helped this friend to study during my masters. I can`t say I had problems doing it, I like sharing and helping others. Yet I could have spent that time in a different way but I helped her anyway. I never asked for something in exchange, just helping made me happy. Yet a couple of weeks ago (more than a year after I helped last) I had a question about her city (actually to help another friend lol). I texted and I was surprised that she was more than happy to help me. He replied in less that 10min (faster than googleing it?) and gave me some great insight about how to do something in her city.
She would probably help me even if I hadn`t help her before, but I can tell from the happy she was to help that she felt like giving back some of the help I gave her. That was never my intention but I really feel safer and happier after helping many people cus I know I can trust them and they will be there to help me. It just feel like an investment about anything I can need in the future, and to be honest I don`t feel like I lost anything from helping them... actually I feel happy to myself about having made that "investment" even if I never "take profit" from it