I started playing on gameknot.com because I was looking for my first online website to play chess on. I Google searched and stumbled upon it in September 2008, when I was just getting into competitive chess.
The goal of all chess puzzles is to checkmate your virtual opponent no matter what moves they make (i.e. A forced mate), in the requested number of moves. Some chess puzzles are created from actual chess games played online, and some are purely composed chess problems, sometimes even with positions that cannot be reached in a real game of chess.
1st, this site is a correspondence-only site!
2nd, there is no open forum to improve the site. And you have to pay a 'club fee' just to start your own forum AND become a premium member just to give them feedback!
3rd, there is no mobile app.
4th, there have been absolutely NO major changes to the site for at least the past 3 years. They updated animations but really that is it!
However, there are still some features that gameknot has that are better than any other chess website...
1 Better Tactics Trainer than chess.com
Chess.com times all their tactics, so if you don't solve them in 5 seconds, you lose rating points even though you solved them perfectly!!! This is unrealistic for a real OTB situation where the TC is 40/120, SD/60, d5.
Also, chess.com has a very limited supply of tactics, whereas gameknot actuallyuses tactics played on actual games on their site, so they keep adding more (there were at least 100,000 tactics when the site added the feature several years back). People on chess.com get 2400 tactics ratings even if their OTB rating is only 1600, because they simply memorize the solutions to hard puzzles, and that same puzzle will appear again 10 puzzles later, because chess.com has so few tactics puzzles. Repeat this for many many puzzles and soon your tactics trainer rating is 2400. On gameknot, you cannot cheat the system this way.
2: More things to do in correspondence chess
Gameknot has ladders and leagues. Chess.com doesn't.
3: Bigger games database
Gameknot has many more games in its database than chess.com. For 1. e4 in chess.com's explorer (https://www.chess.com/explorer/), there are just under 700k games. Gameknot's database (http://gameknot.com/chess-games-database.pl) has just under 800k games for 1.e4 !. This is when you switch to the 'world' database. Under the 'gameknot' database (games actually played on the site by players rated at least 1600), there are even more games.
And there you have it! A comparison of chess.com and gameknot. I will do more of these for other websites. Stay tuned!