I wrote an IRC bot[1] to get a feel for Scheme in general earlier this year. I chose Chicken for it, which got me to look into Cheney on the MTA and other implementation details which were really interesting.
The FFI is really nice, given that Chicken compiles to C.
The Chicken IRC channel was a lot of help early on.
All in all an enjoyable experience!
[1] https://github.com/sebcat/kylling/blob/master/kylling.scm