Most management software made for those with that number of units and up will have document creation/signing modules built in. 

We have been slightly less satisfied with their web solution (so called "sites" module).

@Sean Hurwitz I suggest another tool: ProperrtyRadar, founded by another Sean.My friend Sean O'Toole has brought us West Coast investors another indispensable feature that I only discovered this weekend, investment analysis module.

Some of the smartest guys I know still scribble rent payments on the manila folder the lease lives in.Podio is nice, I would like to develop a PM module for it.

I have been using a company called Payclix.for my properties Apartment complexes and Mobile home parks For rent collection any type on fees or deposits  .I Liked the  concept so much I joined their Company .You can go to PayClix.com to see how easy it is and they have an exclusive Accept or Reject Module so you are in total control  You can choose to Reject a partial payment to avoid 3 day notices and evictions If you reject it no harm no foul .They integrate into your Existing acounting system or they can create one for your needs .It's made my life and my property managers lives so much easier.Checks ,Credit and debit cards .A tenant would much rather pay online the night before with a credit card than pay a $60 late fee .With a click of a button .  

One Thing Brie and I are contemplating with Turn Key reviews is to add a PM module for each market as well. so people can get a read on good pm in a market and one's that have issues.. goes hand in hand with picking the best turn key operators out there. 

@Steven Liu,There are resources here on BP, or you can discuss self-directed retirement plans and how to approach private lenders with your financial professional (I'm not one).The education to which I am connected has a full-day module on private money in the beginner's classes ("Essentials").David J Dachtera"Success is not a destination.

Every year to two years there are additional upgrades or modules that are added.

I can't imagine paying $1k on a private money creative financing module will save you money or be worth your while.  

You will have to take a 100 question quiz at the end of each module to show you've done the studying/course work.