Extremely minimal service that listens for Gmail "new mail" push notifications (using the built-in imapfilter), then pops up a system notification (showing you the email sender, subject and body) with sound.
(I wrote this because I couldn't find a barebones system service that configures imapfilter service to use IMAP IDLE with Gmail. The current options are heavy memory-hogging mail clients that support IMAP IDLE, or services/extensions that poll Gmail instead of getting pushes.)
curl -s https://raw.githubusercontent.com/yo-chanan/gmail-imapfilter/master/install.sh | bash
nano -w ~/.imapfilter/config.lua
systemctl --user daemon-reload
systemctl --user restart imapfilter.service
journalctl --user -u imapfilter.service -f
sudo apt rm imapfilter libnotify-bin pulseaudio-utils
systemctl --user disable --now imapfilter.service
rm -rf ~/.imapfilter
rm -f ~/.config/systemd/user/imapfilter.service
rm -f ~/.config/systemd/user/default.target.wants/imapfilter.service
rm -f ~/.local/state/imapfilter-lastuid
systemctl --user daemon-reload