Totally agree with @Stefano_Zamboni
Some of links using search:
http://docs.nethserver.org/en/v7b/webtop4.html
WebTop4 and Samba4 AD on NS 7
Webtop vs sogo thinking
Activesync on WebTop
WebTop groupware on NethServer
Import PST (email, contacts and calendars) to Nethserver / Webtop 4
Development of WebTop5
Enjoy!