Assuming you're in the U.S. (though possibly even if you aren't)...

The cool thing about game mechanics (boardgame, video game, school playground game, etc) is that they're not covered by copyright. And (while this bit might be less true of video game mechanics) they're rarely covered by patents.

So, for the most part, clones require no licensing or anything. You can make a knock-off of Carcassonne or Settlers of Catan or whatever legally, so long as you avoid trademark infringement. (Basically as long as you're careful to make it clear your game isn't by such-and-such company and you don't have any affiliation with them.)

(Also, it's worthwhile to mention that some games are as much or more so "flavor" as/than mechanics. In such cases, while I don't know that there has been that much precent in the court, it's likely the flavor would be considered copyrightable. So maybe if you're copying the BSG boardgame, don't include Cylons. Also, IANAL.)

I once designed/manufactured a 3d-printable clone of Cubed: Next Level Dominoes, which itself was a(n I'm pretty sure unlicensed) clone of The Grid Game.