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There's also open source QTractor, Muse sequencer, Rose Garden DAW

And Tracktion Waveform!

Which is most like FL Studio?

FL Studio is its own thing. If you're used to the workflow there, every other DAW will feel very (very) different.

That said, Bitwig is probably the least orthodox of the others, and so although it is really nothing like FL Studio, that might be a place to start.

ps. I'm the lead developer of Ardour.

LMMS is a lot like FL Studio: https://lmms.io/