oneword is the name of a website with the simple function of writing for sixty seconds about one word chosen for a day. You can also share what you wrote on the site.*
The host and creator, Brian Kessler, had heard of this prompting exercise from a friend in a writing class, thought it was a good idea, and in 2003 programmed it in Movable Type for both his own use and anyone else's. All words are picked by him and are most often not obscure.
You are not obligated to share what you've written, and as such it makes for a nice 'warm-up' to get working on what you actually meant to. However, by entering your name and an email address (the latter is not shown publicly), what you've written can then be read by other users for the day. You don't get a chance to see what the word is before you start, but by not submitting details, the site gives you another try.
Sometimes there are over a thousand entries by the end of Brian's day. Some people type gobbledygook, or paste in reams of swear words; others try word association, or a funny story they remember related to the topic. Still others try poetry (if i'm stuck, my default is a haiku), stream-of-consciousness, or explore a metaphor in short prose.
Try it out at http://oneword.com
*Silly trivia: This paragraph was written in the sixty seconds allotted.