I've been submitting various patches to Sasagawa-san's Easy-ISLisp (EISL) interpreter for the past while. It's got to the stage where I've run out of obvious things to improve, so obviously I would recommend using the language implementation now.
Personally, I think I'll use it for the next while for hobby programming. I'll probably concentrate on applications for the next while. I'm thinking of the following ideas:
I know of code in other languages that does what I want. But given that most languages differ much more than those within the C/C++/Java/C# family, rather than a port a rewrite is more likely. That's fine too, and it's a good reason to pick small codebases to learn from.
Ada entry in a "16k MUD" competition
Simple IRC library & "echo" bot in CL
If EISL can cope with all this, never mind hobby programming it may be good enough to try earn some money from.