In the era of large-scale surveys, N-body simulations are vital in providing predictions on a cosmological setting. In this talk, I will focus on two recent developments made in this regard. In the first, I will present details of an algorithm that speeds-up modified gravity calculations (with a particular focus on the nDGP model), to a level comparable with current LCDM simulations, without any appreciable loss in accuracy. Such a speed-up opens up the pathway to modified gravity simulations on the scale of Gpc volumes, with high resolution. In the second part, I will talk about a new ray tracing code for N-body simulations. Implemented in RAMSES, the code is able to calculate quantities such as lensing shear and convergence on-the-fly, using either the tiling of multiple small simulation boxes or single large simulation boxes to sample the density field as might be observed in surveys. Using the AMR nature of RAMSES, the code is able to achieve high resolution in regions of high density. With the integration of the modified gravity solvers already implemented in RAMSES, we will also be able to make lensing predictions for alternative dark energy and gravity models with non-linear screening mechanisms.