A new Transmission X-ray Microscope (TXM), optimized for in-situ nano-tomography experiments, has been designed and built at the Advanced Photon Source (APS). The instrument has been in operation for the last two years and is supporting users over large fields of Science, from energy storage and material science to natural sciences. The flexibility of our X-ray microscope design permits evolutionary geometries and can accommodate relatively heavy, up to 5 kg, and bulky in-situ cells while ensuring high spatial resolution, which is expected to improve steadily thanks to the support of the RD program led by the APS-Upgrade project on Fresnel zone plates (FZP). The robust sample stack, designed with minimum degrees of freedom shows a stability better than 4 nm rms at the sample location. The TXM operates with optics fabricated in-house. A spatial resolution of 30 nm per voxel has been demonstrated when the microscope operates with a 60 nm outermost zone width FZP with a measured efficiency of 18% at 8 keV. 20 nm FZP are also currently available and should be in routine use within the next few months once a new matching condenser is produced. In parallel, efficiency is being improved with opto-mechanical engineering (FZP stacking system) and software developments (more efficient reconstruction algorithms combined with different data acquisition schemes), enabling 3D dynamic studies when sample evolution occurs within a couple of tens of seconds.