I would like to have an alternative to our IPsec VPN and I am thinking about forticlient. The licence model is a bit obscure: do I need to buy something or the VPN is free? What app should install client side?
Forticlient IS the client side VPN software. You need a Fortigate firewall on the host side.
If you have a Fortigate Firewall, you can use the free version of the VPN client at no cost.
If you want advanced features, you would need to buy licenses for Forticlient EMS.
For a list of advanced features included with paid license see: https://docs.fortinet.com/document/forticlient/6.2.1/administration-guide/269675/feature-comparison-of-forticlient-for-free-and-paid-versions
If you don’t need EMS features, the remote access SSL VPN and it’s corresponding client are free to use with any Fortigate firewall. You would use the VPN only Forticlient available here:
SSLVPN is the way for you to go here I think. It’s free with FortiGates.
As client software, get the FortiClient VPN, it’s also free but comes without support for the client software. Works for both, IPSec and SSLVPN.
https://www.fortinet.com/support/product-downloads -> 4th option in the FortiClient section.
With Forti boxes you usually only buy the warranty/replacement (FortiCare) and the UTM features (FortiGuard) if you use them.