Mobile Apps:
Unofficial Android App
Mobile app developed by user joshmg. Integrated with UpoOPu, Munkbot, and Stinger.
Multi-use Tools:
Utopia Angel No longer updated
Utopia Angel contains intel formatters and various calculators.
Ultima
Bijo's Ultima. Similar to Angel. A nice multi-purpose tool.
Utopia Seraphim
An angel alternative that works with Linux.
Utopia Enhancer
A Google Chrome plugin that acts similar to Angel
Bots
Munkbot
Munkbot will upgrade your User Interface along with providing a fully functional bot that handles just about anything you might want. To get access you Munkbot you'll need to contact munk.
StingerNET
Similar to Munkbot. As far as I know, Stinger is not adding new kingdoms to his service, but I believe there are "open" kingdoms that are not using the bot that you could take, but that will take some detective work on your end.
LucidBot
Java-based IRC bot. Open source. If you're not interested in munk or stinger but would like an IRC bot, this is a possibility.
Communication
Many kingdoms communicate and organize outside of the game's in-game chat and forums. While these methods will vary from kingdom to kingdom, here are some popular options:
IRC
(Clicking the link above will send you directly to the popular channel #tactics using the Browswer-based Mibbit service. No need to download anything)
This is the long-time service that most utopians have used basically forever. The bots are IRC-based. Most kingdoms have public and private channels to communicate in private and also a place where the community can interact with your kingdom and there are also public channels that act as hubs for the community (#tactics, #strategy). Utopia uses the UtoNet server (irc.utonet.org)
If you'd like to download an IRC client, here are a couple popular free ones:
mIRC
Chatzilla (a Firefox add-on)
Many kingdoms have begun migrating to this service as the game as become more mobile friendly. It's a mobile app that allows you to chat cross-platform.
Intel-Storing Sites:
UtopiaPimp
Pimp is the original (redone) intel-storing site. Will store all your in-game intel and track ops/armies.
UpoOpu
A nice looking intel intel storage site with a unique layout and functionality. Not recommended for tablet or phone users, touch-screen limits a lot of functionality of the site.
Other Tools:
Utopia Seraphim Online All-in-One Formatter
Best News formatter out there afaik.
Jillian's Ambush Calculator
A simple ambush calculator
Umunk Target Finder
Munk's target finder. Has lots of filters and sorting options.
eXposed Target FInder
Darkmoore's Target Finder. Very similar to munk's but with some more options.
Social Media:
Player Written Guides/Material
Bart's Mechanics and Strategies
Bart's one stop shop for a quick look on game mechanics and how to use them.
If you have a tool/write up that you'd like to share or think I've missed something important feel free to post or send me a PM :)