I use Transtint diluted with alcohol now, because I use it for my selfbows, but really, the sky is the limit.
Anything that would alter the color of wood could be a stain i.e. blood, iron, walnut shells, dirt, coffee, flower pedals, etc. I have never used these and being a little obnoxious but I could imagine just about anything. Native peoples certainly used such techniques.
Anything commercial is fine, some have better properties as a initial sealant and filler, somewhat; I would seek these qualities and of course, the color(s) that appeals to you.
*** Most importantly make sure your stain is compatible with your chosen sealant.
Kris