My first job in mobile development was during the industry’s first big pass at mobile devices, in the era of PalmOS and PocketPC. The company was called AppForge, whose main product was a set of tools and a VM for building mobile applications in VB6. It was a real challenge, as the devices of the era were extremely limited.
PalmOS devices in particular had as little as 128k of usable memory and perhaps 1-4MB of storage, shared across all applications. The device was roughly equivalent to the first or second generation Macintosh both in hardware and what passed for an operating system. So we had to implement everything down to basic shared libraries and memory management, much of it in raw 68k code. It was a great learning experience, though the company (and that era of mobile hardware) didn’t live long.