TXPPM docs
This software is usable for all RC Transmitters with the PPM modulation (mostly all transmitters with trainer/simulator connector).
Purpose of this one is to convert signal from your transmitter and make it available as joystick in your operating system. You don't have to buy anything else except your transmitter adapter + mono/stereo extension cord for your sound card input ! Or you can make own cable for direct connection into your transmitter with specified TX connector (e.g. mini din 4 for Esky Hobby) and mono jack.
Example scheme:
Cost of this stuff is around $1 and you can find these parts in home too :) For example, DX6i transmitter need only mono or stereo jack (from both sides) cable.
As result you can play all simulators and games which requires joystick interface, for example: Heli-X, CRRCsim, FlightGear, ClearView (with wine, ...), etc.