Fillarivahti records the availability of each bike station in Helsinki and Espoo. The yellow line graphs today's availability, and the gray area shows the weekday's average availability. The black, dashed line visualizes full capacity, and helps put things in perspective.
If you're interested to check out how the site is built, the sources are available on Github. The repository includes the availability recorder and the API for reading them, as well.
Thanks to HSL and DigiTransit for providing open APIs, and to Markus Kainu for collecting historical bike availability data!