Pricing
Freemium
Freemium is a pricing model in which a functional version of the product is free indefinitely, with revenue coming from users who upgrade for capacity, collaboration or advanced capability.
The design problem is where to draw the line: too generous and nobody upgrades, too restrictive and the free tier fails to distribute.
The best free tiers are limited by a dimension that grows naturally with success (seats, volume, history) rather than by removing core value.