iMessage
Used by 20 peopleen.wikipedia.org ↗

“My worst habit is that instead of putting notes in Evernote, like when it TAKES MULTIPLE MINUTES TO LOAD, is that I will text whatever it is to myself, because iMessage opens instantly and even if the text doesn't go through it's recorded on the end of the device where it was written.”
Casey Johnston Interview, Writer, editor · via Uses This 
“iMessage has a ton of flaws, but unified messaging between all my devices is so useful that I still love it.”
Greg Maletic Interview, Developer (Panic), illustrator · via Uses This 
“iMessage: I use iMessage to chat to people during my work day.”
Julie Ann Horvath Interview, Designer, developer (GitHub) · via Uses This