Chess Tactics Server is a great free tool that allow the user to train is tactics online for free!
Currently 23,803 tactical chess problems with a degree of difficulty ranging from trivial to ambitious are provided to be solved against the clock. Your tactical performance will be measured by the Glicko rating system. The problems are rated too.
You can sign in completely anonymous as guest to get familiar with the chess board interface, browse some problems or just look around.
If interested, you’ll just need a valid email address to register and join our community.
Guía de utilización en Español. Thx to GM ICCF Roberto Alvarez
This is a non-commercial service created and supported by chess enthusiasts from our chess club in Berlin, Germany. It is still under construction. Everyone is invited to participate in development. Please don’t use your skills on attacking this server, but on detecting and removing possible exploits.
For help or proposals send a message to the operator.
What CTS as to offer is over 20.000 chess problems for us to solve and comment on them, every service provided by the server is free of any charge the server is quite fast and stable, and they answer support emails quite fast for a completely free service.
The downside of this website in my opinion is the poor graphical interface presented to us, and the little time given to solve the problems, although it is more time then some other tactics websites it still is very short for me.