Super smooth process and no cost to you as the landlord; the applicant pays the screening fee.For overall management, I’ve found Baselane to be the most complete free platform.

As for the residential lease, once you have a prospective tenant and you prescreened them, use Apartments.com for taking in online rental applications and use it as your property management platform - it's free and it helps you generate leases once you approve an application - you can also generate lease renewal and collect rent on there.  

Quote from @Maranda Tucker: Quote from @Jorge Caceres: Zillow is good platform for taking applications and for posting your listing.

Your application will be denied if you apply for any vacant unit. 

Recommend EVERY landlord require W-2 and bank statement from EVERY applicant to try to avoid paystub fraud! 

Did not see another spot to put application feedback.

Is a legal requirement to have a formal application with proof of income, etc?

You could let the current applicants know that you will honor $XXX if they are approved, but that you are changing the list price for any future applicants.

My question is: if I accept someone to rent when do I stop allowing other applicants?

You have another SFR under contract for $700,000 and would like to purchase it with a cross-collateral hard money loan.