Apps like UptimeRobot: Monitor anything!

Downdetector

★3.8

Ping & Net

★4.6

Ping Tool - DNS, Port Scanner

★4.2

Web Alert (Pro)

★4.1

Ping(Host) Monitor

★3.9

IMSO: server status monitoring

★4.2

Site Monitor

★3.6

Web Alert (Website Monitor)

★4.2

sysAdmin ToolBox

★4.2

APCUPSD Monitor

★4.3

AnyTracker - track anything!

★4.0

PingTools Pro

★4.0

Mobile Poller for Site24x7

★5.0

Chat Peek: Last Seen Tracker

★3.4

Domotz Pro: Network Monitoring

★4.1

Pronet Plus

★3.3