Apps like UptimeRobot: Monitor anything!

Downdetector

★3.7

Ping Tool - DNS, Port Scanner

★4.2

Ping & Net

★4.6

Web Alert (Pro)

★4.1

Ping(Host) Monitor

★3.9

IMSO: server status monitoring

★4.3

Site Monitor

★3.6

Server & Website Monitor Pro

★4.1

sysAdmin ToolBox

★4.2

APCUPSD Monitor

★4.3

Price Tracker: AnyTracker

★4.0

PingTools Pro

★4.0

Web Alert (Website Monitor)

★4.3

Mobile Poller for Site24x7

★5.0

Smart Battery Alerts

★4.4

Domotz Pro: Network Monitoring

★4.1