You're probably looking for Karl3DS
(not yet released), then. It does not yet support MSET or spider, but I'm pretty sure they said they were going to port it to MSET at the least, eventually. Other options include OSKA
(not booting into a CFW just yet) and the leaked CFW for 4.x
(extremely buggy, crashes a lot, I strongly recommend against using it for any serious homebrew development).
TL;DR: There's no convenient and cart-less solution for running homebrew on a CFW yet. You could get your hands dirty with the spider exploit, but nobody has been working on turning that into a CFW as far as I know.