What is a good Latin translation for "No Rulers" as an isolated motto? Only thing I can find is Nec Principes.
I think the appropriate word for 'rulers' here is domini. Assuming your mood to be imperative, you could simply say Domini absint : 'let there be no rulers here'.
Or you might address those whom you wish to ban by following Virgil's procul, o procul este profani (loosely, 'begone, begone, you who don't belong here') with o procul este domini, 'be off with you rulers'.
The Romans adopted rules against kings early in their history. For example, in Livy, Book 2:
...iure iurando adegit neminem Romae passuros regnare.
(He bound (them) by oath, swearing that noone would be allowed to rule.)
You can capture this idea in a motto by using the present subjunctive:
Nemo regnet (May noone rule)
To capture your exact idea, you can use the word nullus:
Nulli reges sint (Let there be no rulers)
The sint can be omitted as understood. You can use the word principes instead of reges, however, this use of the word would be typical of later Latin (late imperial and medieval). So, it kind of depends what style you want, do you want a classical style of Latin or more of a medieval style. For a motto, either would work. Since a lot of mottoes were written in the Renaissance and post Renaissance period, they do tend to use medieval Latin forms like princeps for rulers or bosses.