I was brainstorming interesting usages of Twitter and came up with the following:
Has anyone else came up with other non-standard usages of Twitter?
I fail to see the advantage of using a proprietary, third-party chat site in place of an appropriate networking protocol.
One of it is already available for Windows - "TweetMyPC v2.0 lets you shutdown/restart/LogOff and lots more in your windows PC.remotely."
If you were comfortable setting up sensors and such, you could get a microcontroller, hook it up to a twitter feed, and then give it remote commands.
For instance, remote controlled house lights. You could then just tweet "Home lights on GXSDFXV" (The garbage at the end is to prevent real tweets from turning on and off your lights).
I'm not sure this counts as a very practical use (a bit of fun mainly), but it certainly attracted my interest:
Twitter image encoding challenge
The idea of this challenge is to try to encode a picture into a 140 (Unicode) character Tweet. It's quite astounding how much information some of the algorithms posted there can fit into a message.
Matthew nailed the point that all these "applications" just represent a communications protocol between twitterer and remote host, and there are lots of mature protocols you could use instead right out of the box, rather than rolling your own on twitter.
But depending on your situation, of course there could be scenarios in which twitter is the easy way. I have written similar hacks that use e-mail as transport mechanism for automated tasks, simply because corporate red tape doesn't permit us other more conventional means. They can reboot machines, restart processes, post public messages, etc.
Scott Hanselman used Twitter to create an app for ordering a sandwich.
I wouldn't use Twitter in particular for transferring any private information (think about security if someone hacks the account and can shutdown your corporate servers or transfer fake licenses). For that I would setup a private server which implements the open microblogging protocol (like identi.ca) as long as - like others already said - there is another more suitable protocol. For publishing PUBLIC information (heartbeat messages can be considered that, too) I like the idea pretty much. We recently had a very successfull (but unfortunately effectless) E-Petition in Germany where a Twitter account posted the number of signatures every couple of minutes.
I think the main advantage of using twitter in instances like this is its SMS capabilities (and the fact they're free - whereas you can buy services that charge a monthly fee to allow you to receive SMS messages to a HTTP page or something like that).
I'd considered using it to make a little budget app for myself where I could SMS twitter things I'd bought to a private twitter account, similar for tracking petrol usage I was planning on smsing the odometer reading,cost etc in a certain format and capturing it at home to run statistics and stuff on it. There are limitations to it though - like you can only hook up an SMS number to 1 twitter account...
It's good to think outside the box, but don't be too focused on using just twitter because it's cool.
Carsonified are using this to allow people to discover other people sitting in the same room at their conferences.
They label each chair with a tag and then you tweet that tag to an account they have and it registers you on a floorplan on the venue. Users are coloured in on the plan by their interests.
Clever but a bit overcomplicated for my tastes...