Me and a couple of friends (victorsenam, gabrielrc) just developed a telegram bot to list upcoming contests. The bot lists the main contests from Codeforces, Topcoder, Codechef, CSAcademy and (NEW) AtCoder!
Checkout the bot here!
You can use /upcoming to list upcoming contests, and the bot will also remind you 1 day and 1 hour before each contest (this can be enabled and disabled using /start and /stop)
The code is available on GitHub. Send us your pull requests!
Any comments and bug-reports are appreciated :)