Lookup value Other with Prompt
Goal: Have an "Other" value for client's that prompts a user to enter some text.
This rough outline uses the Gender field for a client as an example, but can be adapted to other lookup fields.
NB: This will not allow users to create new values for the lookup list 'on the fly'. It is simply providing a text field that will be stored like other fields.
Add the "Other" value to your gender lookup.
Add a site specific text (short one-line field) or text_area (larger box to type into) field called something like Gender Other (your choice of name).
Add a branch logic form called Gender Other (again, your choice of name) and put your new site specific field on it. Optionally change the Label value of the field to be more verbose than just the field name. You probably don't want to make the field required. If you do, no one will be able to erase anything in the Gender Other field if something is entered and a different gender is chosen later.
Edit your intake form that has the Gender field on it.
Add a Branch Logic block element. Select Gender as the toggle field. Select your branch logic form for the Other option.
Drag the branch logic element up to where the Gender field element is, and drag the field element down into disabled elements. Save.
Test the change.
Optionally rinse and repeat for each form that has the Gender field on it.
Optionally edit your main profile and add the new Gender Other field below the Gender field (assuming Gender is displayed, which it usually is). And if you allow Gender to be edited directly on the main profile, you probably want to allow Gender Other to also be editable.
Optional, but fancy: If you want the branch logic to be performed when someone edits Gender on the main profile:
Create an auxiliary form called something like Edit Client's Gender and check the box to create a process at the same time. Put a Branch Logic element on it, pick Gender Other as the toggle field, and pick your previously created branch logic form for the Other option. Save.
On the Processes tab, make sure your new process is Active.
Back on the main profile, find the Gender field, and select your new process in Start Aux Process. Do the same for your Gender Other field. What that will do is call the auxiliary process when someone clicks the Gender label (or the Gender Other label) to edit on the main profile. It will display your shiny new form, and do the branch logic like your intake form.