Please can any one assist me?

I am doing a audit on some Linux servers about 40.
One off the recuirments is a list of Applications currently
running on each server.
Does anyone have a command that I can use to show the required
info?

This is Linux preschool.....

ps aux, top (htop, atop), ...

A good start would be to simply run "ps -ef" and see what processes are running. You could do "ps -ef |grep -v root" to determine those processes not run by the root user. Generally speaking processes run by root are system processes and applications have their own admin user. Unfortunately this is not always the case - many people badly configure systems and have root running applications it shouldn't. There are also special cases where the first process is running as root and it then spawns subprocesses as another user. (Properly configured Apache is a good example of that.)

Many packages on Linux are installed by a package manager and these are different for the various distros. You could use your package manager to show you what packages are there and then try to determine which of these are just system (required to support the application) or are actually the main point of the server. For example you could run "rpm -qa" on a RedHat/Fedora/CentOS system to see all RedHat Package Manager (RPM) packages.

Some packages however are installed by other means - via an extracted compressed tar bundle and/or compiled locally on the server.

I guess it would depend on what the definition of "application" is in this context. Were I charged with doing such an audit my definition would be:
1) Primary purpose application of the system whether it is free or not.
2) Any commercial application (one you pay money for).
3) Some other applications critical to the business whether free or not.

I suspect the main interest in such an audit is number 2 so I would be sure to list any free applications as such.

So if the primary purpose were to be a web server I might list Apache as the application (seen as httpd in ps output) but note that it was Free Open Source Software (FOSS). If I were running MySQL as a primary database server I would list MySQL.

If I were running say Oracle which ships with Apache I would list the Oracle product but not Apache as I would consider it part of Oracle install. (Similarly Oracle is heavily dependent on Java so I wouldn't list Java as it is FOSS.)

If you were running JBOSS as supported by RedHat you might list that as an application even though it is part of your web infrastructure.