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) is configured as (external) engine.
The Mac-version can be downloaded here: informatrix.ch (9-'12) ; the engine is programmed in C (since vers.1.5), while older versions had the engine programmed in Java and could also play on Windows or Linux.
Interesting: it can be configured to have the GUI with Swiss dialect of German (Schwiizerdütsch: "Elektroneghirn" for computer, "Spile mit Pschiisse" for takeback allowed)
At informatrix.ch they write, that Jacqueline Go (2.1) has a built-in engine for 9x9 games. Older versions of this program had the built-in engine coded in Java, which showed continually the current score.
You can view ("and edit") simple sgf files (vers.1.3: one branch only).
Use Jaqueline Go in Linux and Windows
Apparently the downloadable file (.dmg) is for Mac systems only. But there is a trick: use the 7zip program to unpack the .dmg-file. Dig in the folder you got and you will find Jacqueline\Jacqueline.app\Contents\Resources\Java\jaquelineGo.jar. This is the file you need: you got Jaqueline Go 2.1 and can run it with your current Java. Apparently this version has no built-in engine (or it cannot run in Windows/Linux), so you need to configure the program to find your local GnuGo.
At informatrix.ch they write, Since Jacqueline Go can only play 9*9 Go, you must select Gnu Go as a player, if you want to play 19*19 Go. Seemingly this engine is not coded in the .jar file, but separatey and in the C language. -- RueLue