Licenses are perpetual. They do not expire and do not need to be renewed.
Licenses can be upgraded. You can upgrade to a more expensive license later paying only the difference in cost.
Pay attention to the distribution type - Hosted (sites / servers), binary (applications) or source (includes all the others).
Choose according to your needs (more below).
All licenses allow commercial use unless otherwise indicated.
WaterSpout is a lightweight web server capable of handling WebSocket requests. When used as part of an event-driven server pair, WaterSpout enables real-time communication between the user's browser and the server using WebSockets or long polling. The reduced overhead as well as the specialized nature of the code running on the WaterSpout server make for extremely efficient communications between the user and the server.