Below are links to different useful documents and tools that I have come across.

# Resource Description Link
1 Cisco Call Detail Records Codes Common codes that can be viewed with Call Detail Records Link
2 Cisco Collaboration Systems Release Compatibility Matrix List of Cisco applications and their compatibility based on different versions Link
3 Cisco IOS Configuration Fundamentals Command Reference This document contains Cisco IOS commands that are supported in many different software releases and on many different platforms Link
4 Cisco IOS Voice Command Reference This document contains Cisco IOS Voice commands that are supported in many different software releases and on many different platforms Link
5 Collaboration Endpoints Information about Cisco endpoints ranging from IP phones to web, mobile, and desktop clients Link
6 Packet Capture on CUCM How to collect packets sent to and from the network interface on a CUCM server. This also applies to other applications such as CUC, UCCX, CER and IM&P Link
7 Quick Reference CLI Commands for Cisco UC applications This page contains a list of all Cisco CLI commands and their syntax in brief format. Even though the website does not specify versions past 10.x many of the commands still apply Link
8 RTMT Trace Locations via the CLI This document maps the RTMT checkboxes to CLI file locations Link
9 UCCX Historical Reporting Guide This guide describes all the fields in a historical report Link
10 VoIP Per Call Bandwidth Consumption This document describes voice codec bandwidth calculations Link
11 Volume 1, UCCX Getting Started with Scripts Provides an overview of the Cisco Unified CCX and the Cisco Unified CCX Editor web interface Link
12 Volume 2, UCCX Editor Step Reference Describes each individual step in the Cisco Unified CCX Editor palettes Link
13 Volume 3, UCCX Expression Language Reference Provides details on working with the Cisco Unified CCX Expression Editor Link
14 Audacity Easy-to-use, multi-track audio editor and recorder. Useful when creating Music on hold prompts or prompt for UCCX Link
15 CSR Decoder And Certificate Decoder Decode CSRs (Certificate Signing Requests), Decode certificates, to check and verify that your CSRs and certificates are valid Link
16 Cisco Tools & Resources Browse the many tools available from Cisco. *requires cisco.com account Link
17 Cisco UC Answer File Generator Generates answer files for unattended Cisco UC installations Link
18 Cisco Unified Communication Tools This page is a collection of free Cisco Unity and Cisco Unity Connection related tools Link
19 Collaboration Solutions Analyzer Allows you to troubleshoot and validate your Cisco Collaboration deployments Link
20 Convert Audio Online Convert Audio to PCM ulaw 8000Hz Link
21 CUC OVAs Used to build CUC virtual machines) Link
22 CUCM OVAs Used to build CUCM virtual machines Link
23 Data conversion Converts Bytes to Kilobytes to Megabytes to Gigabytes to Terabytes, and vice versa Link
24 Diagrams.net Free online diagram software for making flowcharts, a great Visio alternative Link
25 File Transfer Time Calculator Determines how much time and bandwidth it takes to move large files around a network Link
26 Free Text-To-Speech Converts your Text into professional speech for free. Very helpful when creating prompts in your lab environment Link
27 freeFTPd Free sFTP server Link
28 Greenshot Free screenshot tool optimized for productivity Link
29 ISO Creator ISO Image file creation tool Link
30 MailServer Open-source email server for Microsoft Windows. Perfect for lab environments. Link
31 Notepad++ Free source code editor Link
32 Putty Popular SSH and telnet client Link
33 Rufus Utility that helps format and create bootable USB flash drives from ISO files Link
34 Solarwinds SFTP/SCP Server Free SFTP server Link
35 Solarwinds TFTP Server Free TFTP server Link
36 TranslatorX Allows you to quickly parse through CUCM or CUBE trace files Link
37 UCCX OVAs Used to build UCCX virtual machines Link
38 WinImage Enables you to create floppy images for your virtual machines. Works well when performing unattended Cisco UC installations. Link
39 WinMerge Useful tool that can determine the differences between two files Link
40 WinSCP Free SFTP and FTP client for Windows Link
41 Wireshark Free and open-source packet analyzer Link