Koinos is free to use because of the mana system. If you have 1 Koin then you have 1 Mana, and you can perform any actions you want that cost 1 Mana or less.
When you use your mana, it isn't gone forever. It refills over time ("5 days" has been thrown around, but the amount of time can be adjusted by the community once mainnet goes live).
So, holding any amount of Koin entitles you to free actions on the blockchain forever.
But what about people who don't hold Koin? They can still get free transactions through 2 methods:
- mana delegation
- receiver pays mana
More on these tomorrow,
P.S. I'm interviewing Andrew Lavine (CEO of The Koinos Group) for the podcast tomorrow! Hit reply and let me know what questions you'd like to hear discussed.