Close button sends client to the tray, statically linked Qt for OSX.
See the Changelog for list of features and fixes currently only available in the nightly builds.
To see what changed in the latest release, check out the Changelog.
Important note to Windows 8 and AVG users: AVG is known to cause SoulseekQt to freeze repeatedly. The only known solution is to uninstall AVG completely.
If you're looking for the original Soulseek client (Soulseek NS), please go here.