Reminder Bot is one of my largest ongoing development projects. Reminder Bot is the Discord Bot for issuing reminders (the largest reminder-based bot on DiscordBots.org). Currently, it is on over 4'000 guilds and has 50 donators backing it up, plus 3 translators to help increase the availability of the bot.
The source of Reminder Bot is all available in it's GitHub organization. This includes translations, the web interface, the bot itself and other bits and pieces.
More information and links available here