1. I built a small web app to provide a cycling routine to help me go from zero miles and overweight to riding a century (100 miles) this summer. I used to ride move frequently when I was younger and my longest ride was 87 miles with camping gear on my back. But 2 decades, a web dev job, and 2 kids later I am lucky to be able to get 10 miles per week for any consistent stretch of time. The app takes my recent riding skill and athleticism, and creates a 6 week riding 'program' for me basing itself on # of miles per day for the 6 weeks and increasing each week until the culmination of the 100 mile ride, allowing for 2 rest days each week. It isn't the most robust but it's gotten me motivated to ride this summer.
2. I built a reading list tracker that I can add the books I want to read for myself and my kids. It suggests which book to read next if I can't decide. It tracks # of books to read, # completed, # of pages & hours to read (so I can see how unlikely it is that I will ever finish my list or can plan time accordingly to know through the list systematically), allows me to categorize the books, and lists them as MY reading list or a list to read with my KIDS.
3. A European travel planner that I track country and city costs with, can create custom travel itineraries, which then will show actual costs for the itinerary based on the costs I am tracking/inputting for cities/countries/attractions.
4. More fun for myself and friends: A soccer scores predictor game. We each follow teams and clubs from various world leagues, and pick the scores for upcoming matches. Then the app scores us based on our predictions and we have annual competitions with each other. I built this before these were as popular as they are now, and well before the likes of FanDuel/gambling sites.