I worked on the whole stack.  I built Java/J2EE front ends with Native and PL/SQL middle and top tiers.  I did everything from device interface (Card Readers, Coin Dispensers, Registers, et.al) to writing native server code to writing PL/SQL stored procedures on the backend.

I laid down and managed the file systems on NetWare for several years.  This included writing low leverl file system primitives and providing the interface to manage it.

I would take fluoroscopic images from X-Ray tube and package and send them over DICOM base networks.

I wrote reverse proxies to manage web content via Novell  eDirectory managed ACLs.