For example, there's the form of Democratic Socialism I propose above: where we replace the current business structure with worker cooperatives funded by regulated loans or crowd sourcing that compete with each other in a free market. We know worker cooperatives work, because there are many successful worker cooperatives operating well in the current capitalist economy. There's no reason to believe they would stop functioning well in a free market economy where all businesses are worker run.

That's just one example. The next system project has collected a number of additional ones: https://thenextsystem.org/systems

And like I said, I have a whole bookshelf full of alternative proposals. Some of which don't make a whole lot of sense. Some of which are very plausible. And some of which are already working in micro, just waiting to be tried in macro.