The new trend of CIM

In the last few years we have seen the trend of BIM (Building Information Modeling) where a building is represented using real-world entities instead of a bunch of lines.
This trend is now making a shift in the way architects present their ideas and interact with their models (using software like Autodesk Revit, ArchiCAD and Vectorworks instead of AutoCAD and Bentley Microstation).

BIM would be a great answer for Architects.

But more recently a new term was coined, CIM or the City Information model, which aims to transform the urban planners way of handling their plans just like architects.
Some little known applications has started to explore the concept of modeling the whole urban environment and how much information can we extract from such model, in essence how the model would reveal relationships previously little known to the planner or very complex to map such relationships.

CityCAD 
CityCAD from the British Holistic City Software aims to become the city planners main tool (where they previously relied on GIS systems, AutoCAD drawings or even paper maps and census tables).

See CityCAD Software: Stop Masterplanning! (from The Pop-Up City) and Visualizing and Analyzing Plans with CityCAD (from Planetizen).
CityCAD as a software is more into the space and green planning paradigm, and is currently less into the social, socioeconomic and demographic aspects of the city, but quite frankly these are very complex subjects that need much more research on how to model them and how to turn such issues into solvable questions that a model (and the dataset that we feed into that model) can answer.

CityEngine 
CityEngine from Procedural is more into visualizing the 3D city than assisting in the city planning tasks, but a city-optimized visualization tool is very beneficial to urban planners and would bring the city planners some part of the technology that they always wanted, that to visualize the city's current state to better understand it visually, and to visualize the post-plan state that represents their work (to analyze the plan visually).

See New York City In 2259 (from The Pop-Up City).
Some very irrelative point I like about CityEngine is that it uses the Eclipse RCP Platform (which I like but have nothing to do with the software itself).

Other attempts
Maybe one of the older attempts is the The Open Planning Project, it tries to use the Open Source model to create a community of contributers to create an open solution for city planning.

But this list is very incomplete and doesn't touch on the positive aspects of using a systematic way on handling city planning tasks verses the negative impacts using a limited mindset system to solve a very open-ended problem, and the subject needs many more posts other than this one.

[First Image from Wikimedia Commons]