Network analysis by CPM and PERT method was proposed in the fifties.  After fifty years of use one still finds that majority of projects are prone to delay.   Dr. Goldratt proposed the concept of critical chain first time in 1997 to improve upon the idea of the network analysis. 

Goldratt defines the Critical Chain as the longest chain of tasks that consider both task dependencies and resource dependencies. This is different from the definition of the Critical Path, which is defined as the longest chain of tasks based upon task dependencies. This is a subtle, but important difference. Critical Chain recognizes that a delay in resource availability can delay a schedule just as a delay in dependent tasks.

In Critical Chain Planning mode, one develops a plan backwards in time from a target end date for the project. This focus on completion date is natural.  In traditional Critical Path scheduling, the tasks are scheduled as-soon-as-possible (ASAP) from the project start date. This scheduling places work as close as possible to the front of your schedule. In Critical Chain planning, the tasks are scheduled as-late-as- possible (ALAP) based upon the target end date. This as-late-as-possible scheduling places work as close as possible to the end of your schedule.

Critical Chain task estimating requires a change in individual and organizational behavior
to be effective. One wants to remove the hidden safety in the task durations Now, because this safety is hidden, one has to establish an organizational culture that removes the fear of exposing this safety and removing it from task estimates.

After taking out the safety from the tasks one forms a pool of this safety and place it as shock absorber buffers at key points in the project.  These buffers automatically contract when they are pushed by overrunning tasks and absorb the overruns without affecting the target end
date.

There are a few software packages available to generate and manage a critical chain network.  Some of the examples are provided.

Prochain:  Prochain was the first and one of the leading product in critical chain scheduling.  ProChain provides advanced capabilities for creating integrated project plans, resolving conflicts, focusing on key tasks, and creating and maintaining reliable critical chain schedules.  Prochain is integrated to Microsoft Project.

PS8:  PS8 from Sciforma company is a standard product in critical chain scheduling.  PS 8 provides a robust implementation of critical chain, including planning backwards from a target end date, removal of resource contention, critical chain identification, automatic buffer calculation and insertion, and automatic buffer absorption during project execution.  These features are seamlessly integrated into PS8.  Multi-project critical chain is supported, including synchronizing of project portfolio based upon project priority and loading of key resources.  A buffer incursion curve is from PS8 is presented.

 CC Pulse:  cc-Pulse assists the project team in making a feasible schedule, immunized from the effects of variation with project buffers (Project Tolerance) and feeding buffers (Component Tolerance). The end of the project buffer or project tolerance denotes a protected commitment date for the project’s customers. And once project duration is established with cc-Pulse and the leadership determines the project sequence, cc-MPulse (multiple project management version) staggers the projects on the timeline; reducing work in process to levels the system of resources can process at full speed.

The Looking Glass module  of CCPM is a graphical executive information system; a dashboard, that brings Statistical Process Control (SPC) and buffer management to the world of project management. The Looking Glass presents a graphical multi-project view that allows executives to assess at a glance the state of their multi-project system.  A view of Looking glass is presented herein.