PhaseBot is a bot I have been making over the past several months. He is not a mod, but a clean-room implementation of a Minecraft Client. He will run on any 1.8 server, and has many features. He can do anything a normal player can do, and at much higher speeds. He can also load scripts, written in an assembly-like language, which have access to all of the features of PhaseBot.
To interact with PhaseBot, you simply need to PM him, or chat using a special prefix. He can pathfind using A*, move in any direction, dig blocks behind walls, and place against any block. He can run commands like a normal user, and do anything a normal user can do. Scripts are an easy way to run multiple advanced commands. Here's an example of a script:
More and more features are being added to PhaseBot everyday. You can find the source code on GitHub. If you have any feature requests, you can make an issue on the repo.