Curl Keeper is neither a gel nor a leave-in conditioner, it is a frizz fighter that is usually used under another styler. It's like a silicone-free anti-frizz serum. Most people use it under a gel or cream styler because it doesn't have much hold on its own. However, there have been a few people on the board who have said that they can use CK all by itself and it does have enough hold for them.
Faith, 3Aish redhead
Mama to two wild superheroes and a curly-headed baby boy
Any gel I've ever tried has worked well with curl keeper. CK combined with re:coil and possibly a tiny bit of gel gives me ringlets/clumping and a lot of hold. CK isn't an oily type serum like the john frieda frizz ease or anything though. I use it on wet hair and it almost looks like it's a thick water.