After evaluating IRM, exoPhpdesk, spiceworks and free demo helpdesk software’s.  I found GLPI from freshmeat.net is one of the best among all these. It got almost all the functionalities offered by other commercial help-desk software’s. I have been using GLPI successfully for more that 10 years. I can say  this is the best open-source IT helpdesk and Inventory Management software in the industry

You can download the software form official GLPI webiste

Also you can find the step by step Installation Procedure

Best free Inventory Management software

License –  GPL licence
Features list of GLPI

General

• Multi-entities management (multi-park, multi-structure)
• Multi-users management
• Multiple Authentication System (local, LDAP, AD, Pop/Imap, CAS, x509…) and multiple servers
• Multilingual management (22 languages available )
• Permissions and profiles system
• Cache and Pagination system
• Complex search module
• Bookmark search system
• Configurability of display fields in lists
• Export System in PDF, CSV and SLK (spreadsheet)
• Saving/restoration module of the database to the SQL format
• Exportation of the database to the XML format
• Configurable dropdowns
• Dictionary
• System of notifications on events (consumable stock, expiry of contracts and licenses)
• Updates check system
• UTF8 interface
• HTML 4.01 compatibility

Inventory

• Import data of the inventory from one or several OCS Inventory NG servers
• Inventory of the computers fleet with management of its components, disk space and TCO management
• Inventory of the monitors with management of the connections to the computers
• Inventory of the network hardware fleet with management of the connections to the devices (IP, Mac addresses, VLANs…).
• Inventory of printers fleet with management of connections to the computers and management of consumable associated and consumption and the thresholds of alarm.
• Inventory of the external devices (scanners, graphical tables…) with management of the connections to the computers Inventory of the telephones fleet with management of connections to the computers
• Inventory if the software fleet with license and expiration dates management
• Assignment of the hardware by geographic area (room, floor…)
• Typing models management to make the insertion of equal configurations easier
• Commercial and financial Information management (purchase, guarantee and extension, damping)
• Filing of the materials left the inventory
• Management of the status of the hardwares
• Management of the various states for the materials (in repair…) Management of generic peripherals and monitors being able to be associated several computers
• Management of external bonds towards other applications
• History of the modifications on the elements of the inventory

Tracking

• Management of the tracking requests for all the types of material of the inventory
• Tracking requests opened using web interface or email

Final user

• Final user frontend for intervention demand
• Mail tracking of the intervention demand feature
• Interventions history consultation
• Possibility of adding comments at the request of intervention using web interface or email

Technicians

• Interventions demands priority management
• Tracking of interventions demands
• Mail tracking of interventions
• Assignment of interventions demands
• Opening/Closing/Re-opening of interventions
• Assignment of a real time of interventions
• History of done interventions
• Displaying of the interventions to do by a technician
• Displaying of the history of the interventions for a given hardware
• Posting of the interventions to be realized by technician
• Posting of the history of the interventions for a given material
• Management of planning of intervention

Statistics

• Statistics reports by month, year, total.
• Global
• By technician or enterprise
• By hardware, location or type
• By user
• By category
• By priority

Management

• Management of enterprises (manufacturers, suppliers, conveyors, people receiving benefits…) and associated contacts
• Management of the contracts (loan, hiring, leasing, insurance, maintenance and service)
• Management of the documents related to the elements of inventories, contracts…
• Management of the types of authorized documents

Reservation

• Management of the reservations for the material in affected inventory with the park of loan
• User interface (calendar) for reservation

Knowledge Database

• Management of a basic system of knowledge hierarchical
• Management of a public FAQ

Reports

• Reports generation about the devices
• By device-type
• By associated contract
• By commercial informations
• Network Reports