So I accidentally knocked over another coffee on my desk today. Luckily none of it got on my keyboard or mouse, but it made it wonder - are there any devices that stop this from happening? Like some kind of holder/stabilizer which holds your drink and sticks to your desk so you can't knock it over. Does such a thing even exist?

Maybe purchase a heavier cup/mug and drink through a straw...?

I have a pretty big mug, it's always my left arm I knock it over with.

Maybe place your mug on the right-hand side of your desk/table (away from your left arm), or get a bigger desk/table ?.

Good idea, I feel stupid now (though I'm sure I'll still find a way to knock it on that side too)

Look at "Mighty mug"

Well, I made those suggestions (mainly the second two) because I always have a cup of coffee near me when at the computer, but have only ever knocked it over on one occasion (destroying a laptop). Since that particular incident, I have made it a regular (important) habit to place said coffee cup/mug far enough away from me, and anything important/valuable to not let anything like that ever happen again. So far, it's worked... :)

Seriously? Cup holders are already invented.

Lol, just remember not to accidentally close the drawer... o.0

This style of mug is what you use when sailing/boating/working on seagoing craft when there is a chance of rough seas and you don't want your coffee spilling. I can personally attest to it being nearly impossible to tip over.

Yup, or take measurements, design a holder that has a wide base and fits the cup in question, and find someone with a 3D printer to manufacture it (there are online services and communities for that if you don't have a friend with a 3D printer).