I don't care where this topic gets moved. I am putting it here to hopefully avoid bothering people with this idea that I've had for a really long time. We keep talking about planetcrackers, but we haven't gotten an idea down. So here we go.
The game we have now has certain ways of making planets unusable, such as with nuclear weapons or related AI types. These are fun, but they are not what I'm talking about. Why? Because a nuclear weapon can be intercepted, certain units are immune, and they are disposable AI progress increases. They don't really affect the game from any other point of view other than clearing out a system of too many enemies.
A planetcracker has existed in a few forms throughout gaming, but it's very rare. The oldest I can remember is the 1980's BBS game Tradewars, which has the concept of creating a planet, building a base, and turning it into a mobile battle station that can (slowly) be moved across the galaxy to make war upon other players or groups. You had to colonize the planet (introduced risk during transport of being discovered or hostile aliens holding you up), bringing materials for base building, setting up a starport for trading, putting on cannons, interdiction… It was all creating what amounted to a space station of doom. This is a planetcracker, from a reverse perspective.
Another planetcracker, the Death Star from Star Wars. Again we see the colonization, the gathering of materials, the mobile space station being positioned throughout the galaxy to destroy civilizations. In the first Star Wars, the Death Star is discovered which leads to its downfall.
Can you see the difference between a nuclear weapon and a planetcracker? You are building a space station or similar device, investing in it, carefully positioning it, trying to avoid discovery, improving its artifacts, so on and so forth. A planetcracker isn't a missile, it's an investment that you build over time into an impressive weapon of doom, all the while introducing risk to yourself through those activities.
The Fallen Spire campaign has a lot of this sense of risk and reward, gradual investment in weapons and units, building up a small civilization before the winning step at the end.
I'm thinking for a planetcracker, the ability to create and colonize a space station, something that maybe has time limits on it. Maybe it actually takes five hours of in game time for cannons to be operational. Maybe you have to locate colonists and bring them there (this is when I wish AI War trains were like trains). You could redirect the trains to the colonists and your space station and try to protect the supply line over so many hours or something. Or maybe your planetcracker is fully customizable, and it's only as awesome as you want it to be. You can search out gravitational thrusters for it to be mobile. You could search out materials to attach turrets or defenses. It could be a defensive planetcracker, or an offensive powerhouse. You could attach a gravity drill or maybe a black hole machine.
The planetcracker should be obvious now that is something way beyond a missile and is a lot closer to creating a planetweapon.