  We use magnetic helicity to characterise solar wind fluctuations at
proton-kinetic scales from Wind observations. For the first time, we separate
the contributions to helicity from fluctuations propagating at angles
quasi-parallel and oblique to the local mean magnetic field, $\mathbf{B}_0$. We
find that the helicity of quasi-parallel fluctuations is consistent with
Alfv\'en-ion cyclotron and fast magnetosonic-whistler modes driven by proton
temperature anisotropy instabilities and the presence of a relative drift
between $\alpha$-particles and protons. We also find that the helicity of
oblique fluctuations has little dependence on proton temperature anisotropy and
is consistent with fluctuations from the anisotropic turbulent cascade. Our
results show that parallel-propagating fluctuations at proton-kinetic scales in
the solar wind are dominated by proton temperature anisotropy instabilities and
not the turbulent cascade. We also provide evidence that the behaviour of
fluctuations at these scales is independent of the origin and macroscopic
properties of the solar wind.
