Maxwell 1.3 for Mac could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this app available.
Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe. The most popular versions of the application are 2.7 and 1.3. The program lies within Lifestyle Tools, more precisely Bookkeeping & Cataloging. The actual developer of this free software for Mac is Maxwell App Team. This free application can be installed on Mac OS X 10.6.0 or later.
From the developer:
Maxwell is a graphical user interface-based tool for calculating heat loss and heat gain in a building. Gain and loss can be calculated for the building as a whole or on a room-by-room or zone-by-zone basis. This helps users to select HVAC equipment that is appropriate for the climate of Northwestern Pennsylvania.
You may want to check out more Mac applications, such as Skim by the Skim Team, TeX Live Utility or iTeXMac, which might be similar to Maxwell.