Current is a free online diary service that allows you to create a private journal. You are the only one who can see your journal. There is a limit of 140 characters per entry. It is very easy to use. Just type your entry and save it.
This would be great for teachers and students to use for journals. The 140 character limit will force students to be concise and to the point. Students could do screen shots of entries to submit to their teacher for review. Teachers could also use this as a way to keep track of things going on in class.