Here's an abstract tile-laying game from District 31 that looks deceptively simple but which becomes increasingly tactical as the notional modular board (ie: 8 x 8 grid of tiles) fills up.
Designers Stuart Garside and Theo Clarke have included a backstory about the World Geology Society in 1922 but it's pretty much irrelevant and you'll quickly disregard it. This is essentially a colourful abstract game about choosing where to place your tiles in order to score points. Players start their turn with tiles equal to the number of players. These each show the quarter segments of two coloured geodes. On your turn, you'll place one tile and draw another. If your placement completes a geode (ie: adds the fourth quadrant to a geode where three quadrants have already been placed) then you signify ownership by putting one of your marker tokens on the completed geode. The geode will show four numbers; you'll add these and take a 'contract' tile, usually covering the range within which your geode total falls. Your score at the end of the game won't be the numerical value of the geode, it will be the value on the revealed side of your contract tile and that value will be higher where the numbers on your geode exactly match a target number revealed on your contract tiles. This scoring introduces an element of uncertainty over other players' scores. It also incentivises players to try to claim multiple contracts covering the same range as that increases the likelihood of being able to match up contract targets and so maximise your score.
In the main tho', your efforts in the early part of this fast-playing game will be to avoid laying tiles so that you leave a three quadrant geode open for completion by an opponent. In a two-player game, you might push your luck and lay the third quadrant when you know you have a tile that can complete it on your next turn; you're just taking a gamble that your opponent doesn't have the tiles to nab the geode before you do. This game takes up to five players, however, and the more players who have turns before you do then the slimmer the chance that no-one else will be able to complete the geode before your next turn comes around. Gameplay therefore initially resembles the cautious tactical positioning of Othello/Reversi (Ideal).
The game shifts a gear, however, as the imaginary board fills... Players are required to keep their placements within an 8 x 8 grid, which means by about the halfway point in the game, you'll be forced to play a tile to a position that's only likely to help an opponent. You'll also begin to find turns where you have no legal placement for any of your tiles. The rules specify that, in this case, you can play outside the grid to start a ninth row or column which other players can then use. If you still can't place a tile, then you play it face up in front of you and have to place it (along with your normal placement) when, on a subsequent turn, there is a legal position for it to go.
Shown here on Board's Eye View is a preview prototype of the game ahead of its imminent launch on Kickstarter. Art is by Bellafquih Mohammed. We've greatly enjoyed our many plays of this addictive game but we felt it would benefit from a frame or an actual board on which to place the tiles. We gather tho' that this is being addressed in the Kickstarter so that backers will be able to buy a play mat. The published version will also include improved player tokens and a redesign of the geode tiles so that the numbers on them aren't obscured by players' ownership tokens. We hear also that the game will incorporate a solitaire version, so we'll be keenly looking forward to Geode's KS launch. We'll add a link to the KS campaign when that goes live.