There are half a dozen CL implementations, for various purposes:
sbcl, ccl and open source implementations with built in compilers.
ecl is similar, but designed to be easily embeddable in C applications
clasp is a newer one that's built on top of llvm (still unstable, as far as I can tell, but actively developed)
abcl targets the jvm platform and, consequently, can gives you access to all the libraries in the Java ecosystem.
And then there are commercial implementations like LispWorks and Allegro that have their own benefits: Lispworks has, I here, a very nice cross-platform GUI library and, although I don't know much about it, I suspect Allegro has it's own perks.
And, because of the community's emphasis on avoiding implementation-specific behaviors, which implementation you choose isn't that big a deal: I regularly develop a project under multiple implementations, and seldom have major issues doing so.
sbcl, ccl and open source implementations with built in compilers.
ecl is similar, but designed to be easily embeddable in C applications
clasp is a newer one that's built on top of llvm (still unstable, as far as I can tell, but actively developed)
abcl targets the jvm platform and, consequently, can gives you access to all the libraries in the Java ecosystem.
And then there are commercial implementations like LispWorks and Allegro that have their own benefits: Lispworks has, I here, a very nice cross-platform GUI library and, although I don't know much about it, I suspect Allegro has it's own perks.
And, because of the community's emphasis on avoiding implementation-specific behaviors, which implementation you choose isn't that big a deal: I regularly develop a project under multiple implementations, and seldom have major issues doing so.