Microsoft Windows Server administration skills:

Microsoft Windows Server 

Networking: DNS, DHCP, ICS, NTP, VPN, DFS, NFS

Active Directory domain services management and GPO administration

Remote Desktop Services

Little bit use of PS

Microsoft SQL Server administration

IIS services

Kerio WinRoute Firewall and Mail Server

Linux administration

Networking: DNS (BIND, unbound), DHCP(isc-dhcp), NTP, VPN-Servers with L2TP, PPTP, IPSec (MPD, OpenSwan, OpenVPN, Pritunl), NFS, SAMBA, FTP, etc.

Experience in configuring firewalls

Bash

SSL certificates

Apache, nginx

Strong knowledge of SMTP, IMAP, POP mail servers with spam filtering and DKIM, SPF, DMARC support (Sendmail, Dovecot, EXIM, Postfix, SpamAssassin)

Virtualization:

VmWare vSphere infrastructure deployment. vCenter administration.

VMs backup/restore using Veeam Backup and Replication software

Proxmox

etc.

Cloud

AWS, DO, Google Cloud Project, OVH

Other:

Desining and building IT infrastructure in offices

Resolving incidents with software/hardware issues

Diagnostics and troubleshooting of network services and routing equipment

Data recovery

Routers (inc. L2) maintenance and configuration

Experience in Websites (Wordpress, Joomla, Opencart plugins development in PHP)

Ansible

Grafana
Graylog
Little bit SQL

Docker

Terraform