QCAD offers a community edition (free) and a pro version.
If you only need to view (not edit) DWG files, Autodesk offers the (discontinued but still usable) or Design Review . These are small, install-free tools. download AutoCAD LT 2018 portable 64 bit
Once the download is complete, follow these steps to install and activate AutoCAD LT 2018 portable 64-bit: QCAD offers a community edition (free) and a pro version