We introduce and implement two novel ideas for modeling lensed quasars. The first is to require different lenses to agree about H₀. This means that some models for one lens can be ruled out by data on a different lens. We explain using two worked examples. One example models 1115+080 and 1608+656 (time-delay quadruple systems) and 1933+503 (a prospective time-delay system) all together, yielding time-delay predictions for the third lens and a 90% confidence estimate of H₀^-1=14.6+9.4-1.7 Gyr (H₀=67+9-26 km s^-1 Mpc^-1) assuming ΩM=0.3 and Ω_Λ=0.7. The other example models the time-delay doubles 1520+530, 1600+434, 1830-211, and 2149-275, which gives H₀^-1=14.5+3.3-1.5 Gyr (H₀=67+8-13 km s^-1 Mpc^-1). Our second idea is to write the modeling software as a highly interactive Java applet, which can be used both for coarse-grained results inside a browser and for fine-grained results on a workstation. Several obstacles come up in trying to implement a numerically intensive method thus, but we overcome them.

SimpLens illustrates some of the theoretical ideas important in gravitational lensing in an interactive way. After setting parameters for elliptical mass distribution and external mass, SimpLens displays the mass profile and source position, the lens potential and image locations, and indicate the image magnifications and contours of virtual light-travel time. A lens profile can be made shallower or steeper with little change in the image positions and with only total magnification affected.

GLASS models strong gravitational lenses. It produces an ensemble of possible models that fit the observed input data and conform to certain constraints specified by the user. GLASS makes heavy use of the numerical routines provided by the numpy and scipy packages as well as the linear programming package GLPK. This latter package, and its Python interface, is provided with GLASS and installs automatically in the GLASS build directory.