There is a computerised swap system but it has more bugs than a tramps beard- these are being slowly fixed. However, unless you are trying to swap one trip for another which more or less departs and arrives at the same time it is almost impossible. The swap computer knows all the flight time limitations of course but it also has various company restrictions which are not published. You only find out about those when you try to do a swap and it is refused.
Nobody has enough days off to be able to swap them so if you are thinking of trying to swap trips to get enough days off for commuting forget it.
It is better than nothing and it does have a facility where you can "advertise" trips that you want to get rid of, or want to operate. If somebody wants to do a swap you will get an automated e-mail with the details and you just give a yes or a no. You can also search for who is operating a particular trip on a particualr day and try to do a swap directly that way. If we had enough pilots (or fewer restrictions!) the system would probably work reasonably well.