One of the small projects I've been worked on in the year 2015 (alone, as opposed to the Calculator of NMCK) - a web-based application for online testing, which I made for the School of E-procurement (for one Russian company).
The essence of the program is quite simple - you have a variety of tests. Each test consist of a certain number of questions, and each question has multiple answers to choose from - user have to choose only one answer for each question by ticking the right one.
User have a certain amount of time for exam, after which the test ends automatically.
If you look at the screenshot on the left (or at the top, if you're on a device with small screen), you can see the process of passing the test.
In this screenshot, questions 4, 6, 7 and 13 are marked in grey, because user has skipped these questions (didn't answer them) - the user still can return to them some time later, as long as he's not run out of time for the test. Currently, he's in a process of answering the question 31. Already answered questions are marked in blue.
If the user ends the test by pressing the appropriate button, or if the time assigned for the test runs out, the test will be completed - after that the user will return to the main menu to see the results.
User have to answer correctly 75% of the questions to pass the test. To see the wrong answers and to view comments to the questions, user can select the appropriate menu button (this function is not available before the user actually tried to pass the test at least once).
In this "Answers" mode, user can see the results in more detail. Questions are marked with different colors, depending on how the user answered them. If the user selected the right answer to the question - the question will be marked in green, if he selected wrong answer - it will be marked in red, and skipped questions will be marked in grey.
In the same mode the user will see his last answers to the questions in test, as well as the correct answers to questions and comments to the questions, if there are any.
Working on such small project was quite interesting and easy, and the whole creation of the application didn't take much time.