Pushover
Used by 2 peoplepushover.net ↗

“Pushover has been great for allowing my software to tell me when something unexpected or important has happened.”
Waldo Jaquith Interview, Designer, developer, director (U.S. Open Data) · via Uses This 
“I make Pushover, a notification service and app.”
joshua stein Interview, Developer (Pushover, Lobsters) · via Uses This