http://mndlbrt.onekb.net. The link is dead now, so here is a version hosted on this page.
onekb.net offers ultra cheap hosting... if you can fit your stuff into 1024 bytes!
I decided to write a mandelbrot renderer in 1kb. mndlbrt is the result! You can zoom and even share the current image with others (the URL automtaically updates to represent the current area). Also learned a bit about the HTML canvas in the process, which has a surprisingly sane API for webstandards.
https://code.laria.me/mailremind
I've written a web-based service that allows you to send yourself an email based on a schedule: mailremind.
Why? Because I often send myself an email to remind me of something and I thought it would be useful if I could send mails in the future or based on a schedule (e.g. useful for birthdays).
If you also think this is useful, you can have your own installation (it is quite easy to configure), or you can use my public mailremind installation: mailremind.silvasur.net