According to me , a slight difficult OS platform is Blackberry OS because of following reasons :
- Various screen sizes/densities and button layouts.
- Data connection.
Yes, making a data connection is not trivial on BlackBerry. OS
support. Currently foursquare supports OS 4.2.1 (OS running on 4
year old devices) and up.
- Application distribution and updating.
Foursquare currently makes 3 different builds to satisfy varying OS
functionality and API features. Some companies go as far as making
up to 7 or 8 seperate build, one for almost every OS level.
If you have less coding skills, you can start developing an App with Android OS.
There are numerous tools and tutorials which help you to learn Android development.