Is there an alternative feature to Off Mesh Link in NavMesh? Something to make AI easier in the free version on Unity?
There are some alternatives.
First of all, there’s the A* project, which is a navmesh replacement. It has a free version (and a $100 paid version), which apparently has some possible replacements - see this comment on the comparison page. I haven’t used A* myself, but I’ve heard good things, so it’s worth a try.
Otherwise, you may just implement them yourself. Make two paired object, and place them where you want the off mesh links. On Start(), add them to a list of all such off mesh links. Then, whenever you try to find a path to somewhere on the navmesh, but you can’t find a path, loop through the links and check if there exists a path from your position to one side, and from the other side to the target. If there is, move the agent to your side of the link, deactivate it, move it over the link, and reactivate it.
If you know some programming, it really shouldn’t be such a big issue. I’ve done it myself, and while it requires some thinking (especially if you want the agents to move over several links in succession), it’s not that hard of a task.
Not using the built-in NavMesh agent, no. Obviously you could write your own nav system. Or just buy Unity Pro.