  We demonstrate that a lightly-strained germanium channel ($\varepsilon_{//}$
= -0.41%) in an undoped Ge/Si$_{0.1}$Ge$_{0.9}$ heterostructure field effect
transistor supports a 2D hole gas with mobility in excess of 1$\times$10$^{6}$
cm$^{2}$/Vs and percolation density less than 5$\times$10$^{10}$ cm$^{-2}$.
This low disorder 2D hole system shows tunable fractional quantum Hall effect
at low density and low magnetic field. The low-disorder and small effective
mass (0.068$m_e$) defines lightly-strained germanium as a basis to tune the
strength of the spin-orbit coupling for fast and coherent quantum hardware.
