I don't know about software - other than writing your own in a general programming language. Javascript would certainly be sufficient for this kind of thing, and it costs you nothing, and it runs right on your browser. Of course, you need to know how to BOTH program javascript, and see how to convert this problem into an algorithm, for that to do you any good.

The important question to clarify this problem is to know if the numbers must be distinct or not.

The basic idea with kind of of problem is that, once you've chosen 5 numbers, then the 6th number is already determined (as 108 minus the sum of those five).

There are two complications:

1) That 6th number might not be in the range 1-49.

2) If repetitions are not allowed, then that 6th number might be forced to be equal to one of the five numbers you already have.