O&O Defrag Free Edition can merge fragmented files and speed up your system performance and it can also consolidate free space on your hard disks, so new fragmentation can be kept to a minimum.
O&O Defrag Free Edition offers two defragmentation methods:
Optimize/Quick quickly defragments your available files but doesn’t merge the free spaces of your hard disk. This is the fastest kind of defragmentation.
Optimize defragments your files and merges the free space on your hard disk (consolidation of free disk space). This requires somewhat more time but prevents new fragmentation from quickly occurring.
O&O Defrag Free Edition can be downloaded (32bit/64bit) at source here.