I've been working toward a pull up for a while. It's slow going. I used to use my pull down machine but a couple times the cables came unscrewed which made me nervous, which isn't any way to lift.
So lately I've been using handles suspended from a chin up bar that came with the house. (It looks like it should be able to be moved, but we haven't gotten it to budge). Turns out I have reinvented the TRX. But it's a little annoying because I don't have numbers to measure my progress by anymore. But I'll keep pushing.
P.S. another idea I learned from my crossfit days was finding a chest height bar, like at a playground. Feet go slightly forward and you can do a modified pull up that way. That is the posture I use with my suspended handles.