Could you start a company with a co-founder, and have generic agreements in place, all without registering a corporation?
We're bootstrapping our first startup and don't want to spend both money and time on creating a legal structure until we have a MVP.
Some very early stage companies use "Founder Collaboration Agreements." They are very simply and usually address the assignment of IP, future equity shares, and the formation of a business entity. Try googling "Founder Collaboration Agreement" and you'll probably find a few.
As a lawyer, however, I would suggest formation a business entity for liability shied purposes. IT can be done in a simple, cost effective manner. I've seen collaboration agreements get more complicated than forming an entity.
Do define and articulate clearly the roles and responsibilities, equity structure, vesting period and exit clauses.