Jacqueline Go
Jacqueline Go is a freeware player and configurable GUI for Gnugo.
Last version is 2.1; version 1.3 (still a Java program) came with own Java runtime version 1.3 (~18mby), the program (.jar) itself were just 350kby (including 9x9 engine).
Gnugo 3.8 (included in the download) can be configured as engine.
The Mac-version can be downloaded here: informatrix.ch (9-'12) ; it is programmed in C, while older versions were programmed in Java and could also play on Windows or Linux.
Special Features
Interesting: it can be configured to have the GUI with Swiss dialect of German (Schwiizerdütsch: "Elektroneghirn" for computer, "Spile mit Pschiisse" for takeback allowed)
The built-in engine shows continually the actual score.
You can view ("and edit") simple sgf files (vers.1.3: one branch only).