Hello Roberto,
Short answer : Yes, you can trust on Unigui. Its designer is called by the community "the magician".
Long answer :
To be honest, i have not customers who need 1000 concurrent users. But i would like to speak about its hight stability.
1. Fisrt, Unigui is not designed for web pages only. It's a great framework for web applications.
2. For my own needs, I have developped a licence manager ( unigui isapi application), working 24/24, 7/7 since 2016. Very stable. No need to restart the server (rarely, only for windows update). Only few users are using it from internet.
2. I have developped an Unigui application (HyperServer) for a private hospital. The application is working 24/24, 7/7 since march 2018. Also, very stable. 38 users. At this day, never exceed 20 concurrent sessions, as the server is windows 10 (max 20 TCP-IP connexiins, a legacy windows limitation). Soon we will move to windows Server Edition 2016. Firebird 3.0 is continually solicited, more than 5000 transactions by month and the system is very stable. Big boss is hapy and me too
That's all.
3. Oh.... If farshad said you that 1000 concurrents sessions are low load balancing for Unigui today, that is because HyperServer FmSoft technology is rock !. If you see the Unigui 2019 Roadmap, a farm servers is in developpment. Mmm....that promise good surprises !
Best regards.