Astronomy Checklist allows you to keep track of which common nighttime targets you have seen and when you have seen them. It uses Local Storage, a concept new to HTML 5, meaning that data you enter is saved to your browser, eliminating the need to log in. The site is essentially a javascript program, so you should ensure that it is enabled. Use a modern browser!
Basic controls.
You can select which catalogue(s) of objects you which to view with the Catalogue Filter. Click the buttons to toggle. By default, only the Messier catalogue is selected. The Caldwell catalogue makes a good companion to the Messier list, adding 109 more objects of interest to a backyard astronomer. The Visual Binary list contains 50 double stars that are able to be separated by small telescopes. I believe they are all visual binaries, as opposed to optical doubles. Let me know if I am wrong.
All objects have been assigned a difficulty rating (Easy, Moderate, or Difficult). By adjusting the difficulty slider, you can display just Moderate and Easy objects, just Easy objects, or all objects (default). These ratings are purely subjective. I have assigned them based off of several resources.
You can sort your list by clicking the heading (grey box) at the top of any column, excluding the input columns. To reverse the sorting direction, click the heading a second time. You can even sort by multiple columns by holding down shift as you click the headings. The column(s) you are sorting by will be indicated by a different color header. Don't forget, you can sort by difficulty, too.
By clicking the eye icon in the upper right, the page switches into Night Mode. These colors are meant to preserve your night vision if you use Astronomy Checklist while you are out viewing the sky. Currently, the object type icons disappear when in night mode, but the type can still be determined by hovering your mouse over the object type cell. The print button is also removed in night mode.
If you prefer, you may print your list by using the print icon in the upper right. Fill out your checklist by hand, or show off your completed checklist to your friends.
Clicking the Expand button provides more control options, and adds details to the checklist. The object type column will show the full text, and the notes column will become visible. Use this added column however you like.
The Season slider allows you to quickly limit your list to objects that are best viewed during a given season. It does this by setting the right ascension and declination filters to pre-determined values. This feature was designed with Northern Hemisphere users in mind. Equatorial and Southern Hemisphere users should manually adjust the right ascension and declination filters as desired.
You may limit your results by right ascension by adjusting these two range controls. By default, the range in between the two handles is displayed, but by clicking the Invert button the range outside of the two handles can be selected instead. This is useful if you want to, for instance, see the objects in right ascension intervals 22, 23, 0, 1, and 2. Use this filter in combination with the declination control to only show objects that are currently visible in your patch of sky.
Like the right ascension filter, the declination slider limits your results to desired declinations. This is useful for filtering out objects that are never viewable from your latitude, or for combining with the right ascension filter to display objects for a certain part of the sky. Unlike the right ascension control, declination cannot be inverted.
You can run the Astronomy Checklist as a desktop application by going to Save Page As in your browser, and saving it as a complete webpage. You may notice some irregularities with the images, but on the whole everything should remain functional.