I’ve been working on a competitive programming-related website for quite a while now. And I’m now extending my “advertising” to CodeChef!
cp-notes.com is a web application where you can maintain a profile of solved/unsolved problems from several different competitive programming platforms. You can write notes about each problem (with support for LaTeX and images!). If you think your notes for a particular problem are substantial/useful enough, you may choose to publish them so that they will be publicly visible. Public notes can be upvoted, searched for, and will have their own comment section. Receiving upvotes on your public notes will also raise your contribution, for which there is a leaderboard (lol)
I hope that some of you will find it useful!