Been using GreetBot in the past year on a couple of slack groups, does exactly as stated. works great!
It wasn't clear to me that I could setup both a message to an individual user AND to a channel.
I run a group of 1400+ womxn in tech and Greetbot has helped us dramatically welcome new members and provide information on our group with ease. Also love when new features are added (like being added to ProductHunt) I get a ping from GreetBot with the new additions. Thanks so much, this is a great product.