Like the headline says, the Steam version of Dolphin Up has a tentative release date of April 27! I am in the final stages of testing and fixing right now. The steam store page is live right here.
If you are interested in helping to beta test the game as I get closer to release, please drop me a line at firstname.lastname@example.org. It's Windows only for now, but I will be aiming to do a Mac and Linux release soon after, so even if you are on one of those platforms and would like to test, let me know.