You would need a JEE compliant application server for running Appian. Tomcat is only a HTTP server and a servlet container. So you can use Apache Tomcat as a mere web server, with JBoss or other JEE application servers running Appian.

https://docs.appian.com/suite/help/19.2/Configuring_Apache_Web_Server_with_Appian.html

What does Java EE compliant means?

It means that it passes the Java EE Technology Compatibility Kit.

Top 10 Open Source Java and JavaEE Application Servers

<APPIAN_HOME>/deployment/web.war/WEB-INF/resources/appian_log4j.properties

App Server Included!

In this release (18.3) we’re excited to announce that Appian no longer uses a separate application server. Appian now includes a pre-configured version of Tomcat, which takes over the responsibilities that were previously handled by JBoss or WebLogic instances.

There are many reasons why we decided to do this. However, the most important reason is because it removes a layer of complexity when installing, upgrading, and maintaining your Appian environment.

No special license or extra steps required; simply download and run the Appian Installer.

https://docs.appian.com/suite/help/18.3/Appian_Release_Notes.html#removals

KB-1765 Tomcat FAQ

https://community.appian.com/support/w/kb/1190/kb-1765-tomcat-faq

https://httpd.apache.org/download.cgi

http://tomcat.apache.org/tomcat-8.5-doc/index.html

sudo su 
cd /opt/appian/latest/tomcat/apache-tomcat/bin
./version.sh

Using CATALINA_BASE:   /opt/appian/latest/tomcat/apache-tomcat
Using CATALINA_HOME:   /opt/appian/latest/tomcat/apache-tomcat
Using CATALINA_TMPDIR: /opt/appian/latest/tomcat/apache-tomcat/temp
Using JRE_HOME:        /opt/appian/latest/java
Using CLASSPATH:       /opt/appian/latest/tomcat/apache-tomcat/bin/bootstrap.jar:/opt/appian/latest/tomcat/apache-tomcat/bin/tomcat-juli.jar
Server version: Apache Tomcat/8.5.50
Server built:   Dec 7 2019 19:19:46 UTC
Server number:  8.5.50.0
OS Name:        Linux
OS Version:     3.10.0-693.11.1.el7.x86_64
Architecture:   amd64
JVM Version:    1.8.0_232-b09
JVM Vendor:     AdoptOpenJDK

/opt/appian/latest/tomcat/apache-tomcat/RELEASE_NOTES

tomcat/apache-tomcat/RELEASE_NOTES

/Users/azmiratania/Downloads/19_2_0_0_Hotfix_Package_L/updates/tomcat/apache-tomcat/RELEASE-NOTES