Axure RP
A professional prototyping tool with conditional logic, dynamic panels, variables, component libraries, and shareable specifications.
Why use it
Use it to validate lobbies, stores, inventories, and state-heavy flows before engine work, then hand interaction rules to developers.
Where it fits
Use prototypes and playtests to find core experience problems while they are still cheap to fix.
What to check
There is no permanent free plan, collaboration and cloud publishing require subscriptions, and prototypes do not replace engine performance tests.