  We report on the production of a $^{41}$K-$^{87}$Rb dual-species
Bose-Einstein condensate with tunable interspecies interaction and we study the
mixture in the attractive regime, i.e. for negative values of the interspecies
scattering length $a_{12}$. The binary condensate is prepared in the ground
state and confined in a pure optical trap. We exploit Feshbach resonances for
tuning the value of $a_{12}$. After compensating the gravitational sag between
the two species with a magnetic field gradient, we drive the mixture into the
attractive regime. We let the system to evolve both in free space and in an
optical waveguide. In both geometries, for strong attractive interactions, we
observe the formation of self-bound states, recognizable as quantum droplets.
Our findings prove that robust, long-lived droplet states can be realized in
attractive two-species mixtures, despite the two atomic components may
experience different potentials.
