I want to monitor my network devices ( router, switch) in our network for collisions. Can anyone please suggest any open source web application which can be used for the above purpose ?
Unless you have hubs, you should have no collisions.
Any standard SNMP monitor tool should be able to grab collision data from your routers or switches provided they are SNMP capable.
Search the site for network monitoring tools.
Hopefully you're in a switched environment, in which case you shouldn't have collisions unless you've got misconfigured links between your hosts and your switch ports (host at half-duplex and switchport at full-duplex or vice versa), in which case you can monitor the switchport counters, if you have a managed switch that supports per port collision counters.