If you want to hone your skills in regards to curves, colors, code or kerning; Games for Designers has a great collection of creative games, all centered around the design process. The website features a masonry style layout like pinterest, but instead of pins, the columns are full of games. Some of the games are cheesy for sure, but others are quite fun, and a few of them I use when trying to hone my skills or just kill some time. The site is an active repository so they are still adding new games, and if you have one you can submit it via email at the bottom of the page.
A personal favorite of mine is Blendoku (like sudoku but for colors, kind of).
The site is in french (the screenshot above is a Google translation), but all of the games I played were in english.