You can use Metacello:
Metacello new
baseline: 'MessagePack';
repository: 'github://msgpack/msgpack-smalltalk/repository';
load.
If you prefer development branch:
Metacello new
baseline: 'MessagePack';
repository: 'github://msgpack/msgpack-smalltalk:develop/repository';
load.
Hosted on SqueakSource Repository. (http://www.squeaksource.com/MessagePack.html).
From Monticello:
MCHttpRepository
location: 'http://www.squeaksource.com/MessagePack'
user: ''
password: ''
You can also use Installer:
Installer squeaksource
project: 'MetacelloRepository';
install: 'ConfigurationOfMessagePack'.
(Smalltalk at: #ConfigurationOfMessagePack) perform: #load.
Hosted on Public Store Repository. http://www.cincomsmalltalk.com/publicRepository/MessagePack-All(Bundle).html
You can also download parcels: http://code.google.com/p/messagepack-st/source/browse/#hg%2FVisualWorks
Hosted on VAStGoodies.com.
Core: MessagePack. Tests: MessagePackTests.
You can also download .dat files: http://code.google.com/p/messagepack-st/source/browse/#hg%2FVA%20Smalltalk
Hosted on Google Code site (old version).
Zipped: MessagePack-Dolphin.zip. Sources: MessagePack.
Download the zipped pac file: MessagePack-Dolphin.zip and follow the instruction on README file.