I'm really impressed by Factor. It has a lot of the niceties that I like about Common Lisp, like restarting on errors and the compiled-but-interactive development approach. On top of all of this the development environment is presented as a very cohesive package, including standardized project structuring styles, a documentation system and a UI library.

The last time I tried to learn it I stopped because I found the concatenative syntax even harder to parse than s-exprs when any math was involved. I'm giving it another go now.