chainssh is a shell script to smplify the ssh login via multiple sshgateways/firewallgateaways. e.g. connect from homehost via sshgateway to a clusternode with one command.
Cluster101 allows you to run software on many hosts and perform a simple task scheduling. No need to install any software on the hosts (it just runs tasks via ssh). It is typically used for running scientific applications on University campuses.
SimParEx executes a program(command) on many computers (farm) in parallel and collects the results (task farming). Major features: minimal requirements (TCP, SSH, Perl), flexible task definition, web interface.