Advice over signing a Non-Disclosure Agreement for a Software

I am a college student and I require some legal advice over signing a NDA over a software product that I developed. My situation is this: I met a man one year back who runs a company and wanted to venture into a second startup as an IT company. He asked me to work for him, giving me only 5% share though I did all the work of developing softwares. I joined because I just wanted to learn and money was not really a factor. He gave me only INR 2000 a month. For the past one year there was no document about all the works that has been done though this "still non-existant" company has invested a sum of around 1 lac for various requirements of the works done. There is absolutely no document about me joining the company, me having 5% share of the company or that I was to be paid INR 2000 each month. Every thing was verbal, though I did receive 2000 rupees each month for the last 11 months. The man has, again verbally, claimed that this 2000 rupees was not my "salary", but my "pocket money". I cared less of all these because I just wanted to build heavy weight softwares, which I did. Now they want to list us as a company, and are preparing all the papers. I smelled fraud in the organisation and I demanded a soft-copy of the documents 3 days before I sign it, which they are denying. Also, during the last 11 months, I built around 3 softwares which they did profit from, though I never received any money for the same. They are using this softwares on their other company works. Now we are working on a 4th software which is mid-way into development, and I am opting out of the project because they are all frauds. Now they want me to sign an NDA over the source code of the software though nothing, absolutely nothing is documented against it. They claim that they have given me some amount of money (referring to INR 2000) and also their "other" company has invested around 1 lac for the software. So I have to sign the NDA before opting out. My question is, since, nothing, and absolutely nothing is documented till date, except for the fact that, 2 to 3 out of 11 bank transactions for the INR 2000 has been done from the bank account of their other company. I never signed to any of their agreement, as none was presented with, before. What should be my step? Should i sign the NDA? Thank You in advance.