Object Primer
The Application Developer's Guide to Object-Orientation. An introduction to object-oriented analysis and design techniques. By Scott W. Ambler, SIGS Books.
http://www.ambysoft.com/theObjectPrimer.html

Enhancing Object-Based System Composition through Per-Object Mixins
The paper introduces per-object mixins as a new object-level language construct for object-based system composition. Per-object mixins are implemented in the scripting language XOTCL as a straightforward extension of its method chaining mechanism and enables the developer to mix classes into the precedence order of an arbitrary object.
http://wwwi.wu-wien.ac.at/~uzdun/publications/xotcl-mixin.pdf

David Van Camp - Object-Technology Consulting
Independent consultant specializing in Object Technology, offering articles and presentations on Design, Patterns, Design Principles, Reuse, Software Process Improvement, RUP, XP, C++, Java, and PowerBuilder.
http://davidvancamp.com/

SNIP from Cleanscape Software International
An easy-to-use C++ development tool that bridges the gap between design and coding and saves hours of editing/debugging. It also allows developers to specify design patterns as object models, and automatically generates C++ classes from the object models.
http://www.cleanscape.net/stdprod/snip/index.html

Chris Ruel's Object Technology Website
Design patterns, Model-Driven Architecture, object-oriented methodology, and best practices.
http://eyebright.sslnetworks.org/~chrisrue/ChrisRuel.net/ChrisRuelNet.htm

Object Orientation Tips
The most useful and interesting OO posts collected from newsgroups, mailing lists and web forums.
http://ootips.org/

Object Mentor Inc.
Agile and Object Oriented Design training, mentoring, coaching, and development.
http://www.objectmentor.com/

The Technology and Business of ObjectStore
Detailed two-part history of Object Design, maker of object-oriented database management system ObjectStore.
http://dlweinreb.wordpress.com/2007/12/31/the-technology-and-business-of-objectstore/

ObjectPlant
Shareware program for Object-Oriented Analysis and Design. The notation used is based on the Object Modeling Technique, OMT but also supports a subset of the Unified Modeling Language (UML).
http://www.arctaedius.com/ObjectPlant/

F-Script Home
Smalltalk-based pure object-oriented environment to work with Mac OS X software. Innovations: high-level model for object manipulation, powerful object browser. Developed from scratch for the Objective-C object model. Highly integrated with Cocoa, native access optimized. Descriptions, news, documents, downloads.
http://www.fscript.org/