What is the crowd's opinion of JDarkRoom?

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I'd like to double-down on the jdarkroom recommendation. It's a Java implementation of the same idea from White Room or Dark Room, so it should be cross-platform. Plus, there's the added benefit of your program being self-contained in its .jar file.

I've used it for awhile now. It's a great little program. And it even does markdown!

For Windows, take a look at JDarkRoom. On Mac, iA Writer Pro has a lovely Night Mode, but doesn't quite have the retro look you are after.