The quick solution is to update httpd.conf in your main server to redirect traffic for certain apps to different server (or domain). Apache will work like a proxy when accessing other apps. for example, here are sample URLs:

Main Application: http://www.maindomain.com/
Pages of main application: http://www.maindomain.com/something.html
Other application 1: http://www.maindomain.com/wiki/
Other application 2: http://www.maindomain.com/forums/

Here’s what I’ve used, open httpd.conf and add following lines in it:

RewriteEngine on
RewriteRule ^/wiki/(.*) http://otherdomain.com/wiki/$1 [P,L]
RewriteRule ^/forums/(.*) http://otherdomain.com/forums/$1 [P,L]

ProxyPassReverse / http://otherdomain.com/

Details:
Pls make sure that mod_proxy and mod_rewrite are loaded in apache. In above lines:

line 1: Turns on rewrite engine provided by mod_rewrite
line 2 and 3: A rewrite rule to parse the url and detect the word (wiki) in begining of it. if word is there, then rewrite url using different domains (or IP address). The last parameter [P] indicates that its a proxy request.

line 4: URL that needs to be masked while browsing.

Save file, restart/reload httpd service and check. It worked in my case but your requirement may be different, I recommend having of a look of official documentation for url rewriting.