Most sergers can have the cutter disabled, and I believe a decorative type stitch can be made if you fold the fabric and treat the fold as if it were the edge. You sew a narrow or wide stitch, (only use 1 needle on top) then unfold the fabric and pull on it to flatten out the stitching. I haven't used a serger in ages, or tried this, but I understand you can use specialty threads in the looper for effect.