I would say air defense systems. Some can be used in an offensive role but their main purpose remain to defend an area.
Elsewhere, I might be burnt for that but mines (at least regular ground mines) are defensive as well. I can't think of someone throwing a mine at a tank
. The one dropped by planes today are, however, truly offensive especially when they are launched on civilians.
Then, every type of gear that is not truly a weapon : helmets, bodyarmors, and most electronic systems. Radars were first used in a strictly defensive role and Asdic was designed for naval defense.
Interceptor planes is another type. Fighter planes are often used in an attack role but interceptors were made strictly to stop incoming ennemy aircrafts. They are becoming increasingly rare, however.
Tear gas but you might have said it.
Any weapon of course, depending on what end of it you are but that is the obvious
.