Beginning with GParted 0.17.0, there's now online resizing support when using a patched version of libparted, the Linux 3.6 kernel or newer, and a special config flag. There's documentation on the new option in the README but in time the online resizing support will hopefully be common to distributions shipping GParted.
GParted 0.17.0 also supports recognizing Linux swap suspend and software RAID partitions. This open-source partition editor also has fixed busy detection for software RAID and extended partitions. Last but not least there's a systemctl runtime mask fix to prevent auto-mounting partitions.
GParted 0.17 can be fetched from GParted.org.