Lightholm

Lightholm is a single-player tower defence about keeping one lantern lit. Enemies walk the road toward it; you build towers beside the road to stop them, and once the constellation gives them to you, you throw frost, fire and lightning of your own. Waves come at night. Between them the sun comes up, the board is quiet, and you spend what you earned.
Every enemy has a weakness
No damage types, no rock-paper-scissors. Each body is weak to one status: a Runner takes far more damage while Slowed, a Brute while Burning, a Leaper while Shocked, and the plain Grunt learns a weakness to Poison once you unlock it. One tower applies the status, another does the damage, so where you place towers and in what order matters more than how many you have.
Four towers
Arrow - single target, the longest reach, the first tower you own.

Pulse - a ring of damage around itself, the widest in the game, that slows everything it touches.

Fire - a short-range flamethrower. Everything in the cone burns, and burning stacks.

Lightning - chains from body to body and builds Shock until the target is stunned.

Heat
Towers heat up as they fire. A gun that hits the top of its bar jams: it stops firing, vents for a few seconds, and comes back on its own. You can pay to clear a jam at once, or keep a hot gun topped up before it gets there. Repairs are priced against what rebuilding the tower would cost, so maintaining is always cheaper than replacing, and a high-level tower costs like one to keep.
Lantern Arts: five spells of your own
Towers do not have to be the only thing on the board that acts. Unlock the Lantern Arts and five spells sit on the hotbar - press Q W E R T or click the button, then click a point on the road.

Frost Bloom - 18 coins, 12s. Everything in the circle is slowed by up to 60% for up to 5 seconds. Runners are open the whole time.

Emberfall - 32 coins, 16s. A meteor lands after a beat: area damage and up to 4 stacks of Burn. Written for Brutes.

Skybreak - 28 coins, 14s. Area damage and up to 4 stacks of Shock at once, which is most of the way to the Discharge that stuns. Leapers are open while shocked.

Bramble Mist - 24 coins, 18s. A cloud that stands for up to 6 seconds and lays poison into everything in it, every second. Poison makes every direct hit your towers land harder.

Lantern Rally - 35 coins, 24s. Your towers, not theirs: every gun in the circle fires up to 65% faster and makes 40% less heat for up to 7 seconds.

The catch is the price. A cast is paid for out of the same coins as a tower, a level-up and a repair, so every spell is a tower you did not build - and the meteor that saves the wave is the reason the jammed gun stays jammed. Mastery ranks make a cast hit harder; they never make it cheaper or more frequent.
Element pads
Some build sites carry an element, and a tower built on one takes it: Earth adds poison, Fire adds burn, Ice adds slow, Wind fires faster, and Light reaches further and pierces through bodies. The same tower on a different pad is a different tool.
Bosses
Four kinds, and every board's last wave brings one: a single huge body; twins, where the survivor speeds up for good when the other dies; a splitter that breaks into smaller pieces, which break again; and a worm of segments sharing one health pool. A boss takes far more damage only while two of your effects are on it at once - no single tower can manage that alone, which is exactly what a spell is for. A boss that reaches the lantern ends the run.
Twelve boards, three ways each
Twelve hand-built boards, each a different road: straights, lagoons, crossings, a coil, a pinwheel, a compass with four mouths. Every board also carries a build challenge worded against that road - kill the worm before the last bend, clear a wave with no tower on the shared tail - and a time trial. Beat a board and Endless opens on it, with a boss every fifth wave and no last one.

The constellation

A run ends. The board goes dark, and the screen you land on is a sky of 121 stars, eight arms deep, most of them still unlit.
This is where the game actually happens. Every run pays out tokens, and tokens light stars: 538 ranks in all, from a flat five per cent of arrow damage to the doctrines a whole build is named after - slowed bodies carrying current between them, early waves paying a bounty, guns that repair themselves, the five Lantern Arts and their masteries. A lit star reveals what grows out of it, so the tree opens as you climb it rather than showing you the ending on day one.
Nothing is locked in. Refunds are free, always - take a rank back, take an arm back, take the whole sky back and spend it somewhere else, at no cost and any time. Three separate trees are saved side by side, so the poison build and the spell build are one click apart rather than an evening of undoing.
Five things pay for it, and they pay for different play: triangles from every run, squares for clearing a board, a [b]star[/b] the first time you beat one, an hourglass for beating its time trial, and a crown for its build challenge - one each, once. Ten capstone nodes take nothing but stars and four take nothing but hourglasses, so the last third of the sky is bought by playing well rather than by playing longer.
Finish the campaign and you can prestige: the boards lock back to the first, the enemies come back stronger, and every star you lit stays lit.
Also
Call the next wave early for bonus coins - the more of the current wave still unspawned, the bigger the bonus.

Critical hits can chain into multi-crits, each level adding another 100%.

Single player. No microtransactions, no account, nothing to buy but the game.