Silmutaneous users

On stackoverflow, this question would have been terminated because of being "too broad"...

What exactly do you mean

- users sending traffic across the FGT? - unlimited

- SSL VPN users? see datasheet

- IPsec tunnels? see datasheet

- authentication/local users?

... etc. etc.

You get most of this information from the datasheet or the "Maximum Values" list on docs.fortinet.com

If I had to guess...you would mean if the number of simultaneous users is to be licensed, or somehow an upper limit enforced? No, and No.

The hardware performance and capability is the limit in this respect. Very seldom you need to check the hardware related implementation limits, and that's what the "Maximum Values" table is for. Limits depend on hw model and version of FortiOS.

HTH.