AnnouncerBot
Announcer bot lets you know who is joining and leaving chat. No need for any commands, the bot has its own site: https://announcercord.com/
UPDATE 1/24/2022 New UI Announcer bot lets you upload an intro/outro mp3 file and plays it back for your friends when you join/leave chat. There is a discord integrated webapp for you to upload your files: https://announcercord.com/ Simply upload your files, add the bot to a server and you're done. Want to disable playback? Delete the files on the site. The web interface and bot are still in an alpha mode but is expanding every week.
AnnouncerBot is a fun bot for Discord that also covers music and announcements. Its invite asks for no permissions at all. It suits servers of any size, from a small friend group to a large community. No owner has claimed this page yet, so the details come from public listing data. It has been on Discord since 2020.