[KillerRabbitt]

This depends on several factors such as:

1. What are the goals of the project?

2. Are there multiple people involved and do you want a formal corporate structure?

3. Does the project generate significant revenue and will there be tax implications?

4. Are you willing to deal with additional paperwork and overhead?

5. Do you want limited liability if you decide want to borrow money?

[amerf1]

If I was looking to sell my side project as a single founder. Would it be necessary to incorporate?

[tripletao]

Assuming USA: If you're a single founder with no investors, the compliance costs of a single-member LLC taxed as a disregarded entity are tiny, a few hundred dollars per year (depending on the state). That limits your liability, might help deal with some clients, and might make it possible to recognize a sale of the whole project as a capital gain instead of ordinary income.