Question: Is there any way to manually focus the camera on my Android phone?

I know that you can tap on where to focus, but that's just assisted auto focus. What I want is to be able to manually adjust the focus.

Answer: 
There is a free android app that allows you to manually adjust focus (and more camera technical stuff for photographers) 
Its called open camera and can be found on playstore. 
(the one by mark harman) 
NOTE: it will only work if your device supports it. (aka if possible) 

To get straight to using manual focous: 
install, open settings, near bottom of page turn "use camera2 API" on, then in camera mode (ready to take picture) click the "..." on the right side pannel, on the second row down of icons click the "m" (just above the "photo mode" words) (make sure your scolled to top, you can scroll down in that menu) 
It will then popup 'focus manual' and on the left side there is a big slider (above the zoom slider), you can drag that to manually focus your camera. 

* someone who has had this app for a while. 
Your welcome.
Only 8 years later, the Moment Pro Photo app can now do this. May not be available for every phone, but it works as advertised on mine, specifically the manual focus.

<https://play.google.com/store/apps/details?id=com.shopmoment.momentprocamera>