Ran across an article here that listed many available MVVM frameworks. Below is a listing of some of them, but there are some good comments to the original blog posting as well, so I encourage one to visit the original article as well:

Common features:

• ViewModelBase class (for the implementation of the INotifyPropertyChanged interface)
• RelayCommand like class to link UI command to ViewModel’s handlers
• Unit tests comes with the framework

Cinch

• Author: Sacha Barber
• Silverlight support: no
• Documentation: excellent, 6 articles published on CodeProject
• Hosting : CodePlex
• License:  Code Project Open License
• Features:
  • attached behaviors
  • validation suing IDataErrorInfo
  • support for IEditableObject
  • weak events creation and subscription
  • mediator messaging using weak events
  • IOC/DI support (using Unity)
  • services: event logger, message box, open save dialog, popup
  • threading helpers
  • support for menu items
  • closeable viewmodels
  • MVVM code generator

MVVM Light Toolkit

• Author: Laurent Bugnion
• Silverlight support: yes
• Documentation: many articles available on Laurent’s blog + other developers as well
• Hosting: CodePlex
• License: MIT license
• Features:
  • MSI installer
  • VS project and item template
  • VS code snippets
  • Messenger system for inter-viewmodel communication

MVVM Helpers

• Author: Mark Smith
• Silverlight support: no
• Documentation: some articles on Mark’s blog
• Hosting: personal website
• License: not defined
• Features:
  • attached behaviors
  • viewmodel creation using markup extension
  • attributes based validation
  • IOC/DI using ServiceProvider approach
  • closeable viewmodel
  • wait cursor (using new WaitCursor() { // your code here })

MVVM Foundation

• Author: Josh Smith
• Silverlight support: no
• Documentation: articles about the Messenger implementation on Josh or Marlon Grech’s blog
• Hosting: CodePlex
• License: MS-PL
• Features:
  • Messenger system for inter-viewmodel communication
  • PropertyChanged event monitor

Caliburn

• Author: Rob Eisenberg
• Silverlight support: yes
• Documentation: complete online documentation available
• Hosting: CodePlex http://www.mssoftwareconsulting.com/general/refer.aspx?url=www.codeplex.com/caliburn
• License: MIT license
• Features:
  • commands are built on top of Actions and thus share many of the same features, including multiple input parameters, filters and automatic asynchronous execution
  • presenters that handles UI lifecycle issue such as handling activation, deactivation and shutdown semantics for various UI components
  • Caliburn applications are fully testable
  • various utilities such as a background task manager
  • supports various UI pattern (not MVVM only)
  • dependency injection container

Onyx

• Author: William e Kempf
• Silverlight support: no
• Documentation: basic introduction available on CodePlex
• Hosting: CodePlex
• License: not specified
• Features:
  • ServiceLocator pattern
  • ViewModel creation using a custom markup extension
  • UI related services such as IDisplayMessage

Calcium

• Author: Daniel Vaughan
• Silverlight support: no
• Documentation: 2 very detailed articles on CodeProject (part1 and part2)
• Hosting: CodePlex
• License: use, copy, modify, and/or distribute and keep the copyright!
• Features:
  • Module Manager for enabling or disabling of modules at runtime
  • messaging services for interacting with the user from the client or server using the same API
  • Command Service to associate WPF ICommands with content interfaces that only become active when an active view or viewmodel implements the interface
  • Region Adapters for ToolBars and Menus
  • Client-server logging ready to work out-of-the-box
  • Includes modules, such as a Web Browser, Text Editor, Output Window, and many more
  • Tabbed interface with dirty file indication (reusable across modules)

nRoute

• Author: Rishi
• Silverlight support: yes
• Documentation: many articles available on author’s blog (see CodePlex project home page for the links)
• Hosting: CodePlex
• License: MS-PL
• Features:
  • support Blend3 behaviors and triggers models
  • resource locator framework
  • view services: OpenFileDialog, ShowMessage…
  • uses attributes to map View and ViewModel together

Nito MVVM

• Author: Shammah
• Silverlight support: no
• Documentation: no
• Hosting: CodePlex
• License: not specified
• Features:
  • various MVVM friendly implementations of the ICommand interface

Ocean

• Author: Karl Shifflet
• Silverlight support: no
• Documentation: articles available on Karl’s blog
• Hosting: personal website
• License: not specified
• Features:
  • written in VB.Net
  • attribute based validation
  • viewmodel base classes: relaycommand, closeableviewmodel…
  • SQL server data access layer

Basic MVVM framework

• Author: Lester Lobo
• Silverlight support: no
• Documentation: sample application available with the library
• Hosting: CodePlex
• License: MS-PL
• Features:
  • delegating Commands\Keybinding
  • messaging between VM’s
  • handling events as commands with attached behaviors
  • handling dialogs (and more) as services
  • VS code snippets

GoodLight

• Author: Peter O’Hanlon
• Silverlight support: yes
• Documentation: sample application available with the library
• Hosting: CodePlex
• License: MS-PL
• Features:
  • “workspace” management (set of document that can be closed)
  • skin support
  • messaging between VM’s