As a perfect example in the genre of pseudo-games that also play themselves, Crab War pits a swarm of genetically modifiable crabs (the kind that don't necessarily attach to your pubes) against various weird looking reptiles. You, allegedly, are the Crab god, who rules supreme over all aspects of their evolution and can also spawn specimens into existence just by tapping on the screen.
Spawned crabs have a very short lifespan. Just as they come into the world, they invariably head towards the current reptile in line. Once the crabs touch a lip, eye or whisker, they explode and deal damage to the docile creature, which stoically withstands all incoming attacks, only extending its tongue to taste some crab before dying.
Every time you kill a critter you will get a small number of yellow shards, which serve as genetic material, as they're used to upgrade your slowly growing number of crab types. We're not talking about a crab population here. Crabs don't seem to exist beyond the playing field, so to speak.
The first few minutes of playing Crab War can be tedious. There's nothing else to do than tap away indiscriminately to spawn more and more kamikaze crabs. However, once you acquire sufficient loot, you will be able to unlock a queen specimen, which does much more damage on impact and, better yet, spawns automatically! This means you can now rest your weary ankle and merely wait for the queens to do their job. You'll probably want to intervene with some more regular crabs whenever there's a "boss" lizard. These fellows can only be killed within a short window of time but also yield more loot when they finally croak.
In any case, investing in queens is your best bet against carpal tunnel syndrome. However, many unlockables only become available after upgrading your level, which only affects your regular (read: marginally redundant) specimens' performance.
Besides evoking the awkward parasitic problem, Crab War is a decent-looking activity app. I can't call it a game since all you do is tap on the screen incessantly. But hey, at least you're not forced to tap all the time. Actually, you're not forced to play Crab War at all, which is a smart decision if you ask me.