  Orbital motion in binary and planetary systems is the main source of precise
stellar and planetary mass measurements, and joint analysis of data from
multiple observational methods can both lift degeneracies and improve
precision. We set out to measure the masses of individual stars in binary
systems using all the information brought by the Hipparcos and Gaia absolute
astrometric missions. We present BINARYS, a tool which uses the Hipparcos and
Gaia absolute astrometric data and combines it with relative astrometry and/or
radial velocity measurements to determine the orbit of a binary system. It
rigorously combines the Hipparcos and Gaia data (here EDR3), and it can use the
Hipparcos Transit Data as needed for binaries where Hipparcos detect
significant flux from the secondary component. It also support the case where
Gaia resolved the system, giving an astrometric solution for both components.
We determine model-independent individual masses for the first time for three
systems: the two mature binaries Gl~494 ($M_1=0.584 \pm 0.003 M_{\odot}$ and
$M_2=87 \pm 1 M_{\textrm{Jup}}$) and HIP~88745 ($M_1=0.96 \pm 0.02 M_{\odot}$
and $M_2= 0.60^{+ 0.02 }_{- 0.01 } M_{\odot}$), and the younger AB Dor member
GJ~2060 ($M_1=0.60 ^{+ 0.06}_{- 0.05} M_{\odot}$ and $M_2=0.45 ^{+ 0.06}_{-
0.05}M_{\odot}$). The latter provides a rare test of evolutionary model
predictions at young ages in the low stellar-mass range and sets a lower age
limit of 100~Myr for the moving group.
