ASAs can indeed be used as a currency for internal economy.
Creating ASAs for that purpose is quite straightforward.
There are some technicalities around key management and you can learn more there: Could I implement an ASA with it's own custom wallet? - #2 by fabrice
But I believe that the hardest part is to decide what the currency would do and to design the platform.
Once it is done, using an ASA for the currency is quite easy.