For the TF2 servers, I have setup a Telegram notification channel alerting people when there are games going on the servers.
The rules here are simple, every 10 minutes the bot will check and see the player counts. If a server has more than 10 people (or 4 for the MVM server), it'll send a message to the group and then refrain from doing so for another 3 hours.
It's pretty handy if you're looking to play but like, not at your desk or something.
Anyway, here is the group!