Mendeley is closed source.
And drop all the dollar signs. Most of us are professionals and know you have to pay for stuff sometimes, it's not like money is evil or anything. Even open source developers have to be paid by someone somewhere along the line for something, or they'd starve.
You sound like a teenager who's just discovered open source software and are temporarily enthusiastic about it being the best thing ever in the whole wide world, while everything else is brewed from the faeces of Satan. But next month you'll forget it and be on to a new fad, maybe genetic engineering or nuclear power or something.