I pick my thumbnail with my fingernails, or my fingernails with my thumbnail when I'm contemplating various concepts in math and physics, or sit and lightly brush my lips/mustache/beard with the side of my finger.
I do an odd sort of meditative stimming to help me go to sleep, to keep myself from thinking all night, I'll sit and blank my thoughts, silence my inner monolog, then sit and uh... it's hard to describe, kinda feels like trying to make my hair stand up by extending my awareness out through my skull in various directions. If that makes any sense... I'll set up rhythmic patterns once I get the whole brain active that make me think of the way cuttlefish fins ripple when they're swimming, or sit and direct it in various directions, all while keeping my inner monolog silent.
I'd do it all the time, as it's very fun, but visual input cancels the effect, gotta be dark and comfortable.
I sit and lock my feet up against my chair and flex my calves, I try my best to keep from grinding my teeth, actually busted a couple molars that got cracked when my wisdom teeth came in... ironic maybe?
Typing is almost like a stim for me, when I think it helps to type at times, and I'll sit and type on my legs sometimes when I'm thinking.