I just had an interview yesterday, and the recruiter sent me an email saying they wanted to connect with me after the interview and see my upcoming availability. How should I reply? Are they asking if I'm available to be contacted? Should I ask how and when he would like to further discuss this?
They want to keep you in their pipeline in case something comes up.
It is his job to fill positions. You are the "filling" - handy for him to have as many of you ready as he can, it does not cost anything at this point.
How you should reply: Do you want to get offers?: -> Yes, if not then -> No
But don´t wait for them if you are currently seeking a job. May very well never come up with a suitable position.