While most Google apps are still in beta, it's clear that some of them are more mature than others. For example, Gmail has more than six years of development, three years and a half since launch and more features than other "out of beta" mail services. That shouldn't worry people too much because leaving the beta stage is not a sign that everything is perfect (Yahoo Mail is a perfect example, look at the comments from this post).
Google's applications have their own versions and roadmaps, but these are not public. That's why it's interesting to see what versions you would attribute to each Google application: 0.1 should mean a very early release, 1.0 should mean the first major release etc. Here's a list of some important Google apps.
Gmail: released on April 1st, 2004 (interface)
Google Calendar: released on April 12th, 2006 (interface)
Google Reader: released in October 2005 (interface)
Google Docs - documents: Google acquired Writely in March 2006 (interface)
Google Docs - spreadsheets: released in June 2006 (interface)
Google Docs - presentations: released in September 2007 (interface)
Google Notebook: released in May 2006 (interface)
Picasa Web Albums: released in June 2006 (interface)
An example of versioning:
Gmail 2.9 - the old version
Google Calendar 1.3 - needs synchronization
Google Reader 0.8 - better feed management, faster updates
Google Docs (documents) 0.5
Google Docs (spreadsheets) 0.7
Google Docs (presentations) 0.2 - should be alpha
Google Notebook 1.1 - one of the best Google apps
Picasa Web Albums 0.8 - still needs a community
What are your versions and why?
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