[lisper]

Thirding CCL :-) The built-in IDE and ObjC integration are awesome for developing on a Mac. And you can deploy finished code on Linux and Windows.

[TeMPOraL]

Fourthing CCL - it's stable on Windows and fast enough for writing games :).

Also, it's the best free CL for targeting Raspberry Pi - unlike SBCL, CCL supports native threads there, and with the weak but quad-core processor of RPi2, the difference is very noticeable.