The site – http://ereadplus.com offers free apps for your Kindle and is being modified and added to all the time. It already has several fully functioning apps.

Currently there are:

• Calculator optimized for the kindle screen
• Kindle Calendar
• Time Zones
• Latest News Feeds
• Currency Converter
• Units Converter
• Web Bookmarks
• Thesaurus
• Google Maps for Kindle
• Language Translator

Several Kindle apps available from Amazon offer some similar functionality, but these are only available to American users, and of course you have to pay for most of them. The apps on ereadplus.com are available to everyone free.

The thing is: these “apps” are merely a bunch of links to some decent javascripts, problem with them – they will only work in your browser and so for most people outside the US only if they are within range of a WiFi spot.
Nevertheless, it’s worth trying them.