Almost anything. There are a lot of built-in definitions to monitor and/or collect performance metrics on a variety of systems. If your device is not on this list, there may be some community-contributed configurations available—or you can easily create your own.
- ICMP/Ping
- DNS
- DHCP
- HTTP(S)
- FTP
- JDBC
- SNMP
- SMTP
- SSH
- WMI
- WSMan
- Cassandra
- MySQL
- PostgreSQL
- MS SQL
- Oracle
- VMware
- Elasticsearch
- Windows and/or Linux servers
- NSClient
- Prometheus
- 3Com
- APC
- Brocade
- Cisco
- Dell
- ExtremeNEtworks
- F5
- Fortinet
- HPE
- IBM
- Juniper
- Mikrotik
- Netapp
- Palo Alto
- Sonicwall
- ...and many more