Gah where to start... anything capturing flow (it won't work, you are going to have to deal with massive volume with really little head), vertically oscillating elements anchored to the seabottom driving pistons, impellers driven by waves trying to enter constricted passages, horizontal device driven by waves running up the tidal grounds, under water turbines of all sorts, shapes and sizes, scissor arrangements (with or without floats attached to the far end).

You can broadly group all tidal devices into several simple groupings and for each of those there were a number of initial prototypes and all of those did not make it past the POC or initial deployment. Anything the future is likely to come up with will be variations on those themes. That won't stop people from trying and it won't stop future subsidy grabs because this all falls under the 'wouldn't it be nice if it worked' heading. Yes, it would be very nice. But no, it doesn't work and if you're not going to come up with something radically new you are better off reading the literature on what exactly made it not work the first time.

Those who don't know history...

Here is a very nice example:

https://teamwork.nl/category/teamwork-technology/

I'm sure they pocketed a ton of subsidy by now.

In the same vane (pun intended): rooftop windmills, vertical axis turbines, kites, sound to energy conversion and on and on.