In addition to the picker listed here, you can create your own company pickers using the Company Picker data definition.
Data Element Name: otherCompanyID
Label that will Appear on the Form: Company
Available for Forms on Mobile Device: Yes (iOS & Android)
What it Does: Use this picker to choose from a list of partner or member companies. Unifier populates this picker with the names of the companies in the database. At the company level, the picker will show partner companies. At the project level, the picker will show member companies.
Note: Do not use this picker on configurable manager attribute forms.