Yes, you can create new modules in SplendidCRM. SplendidCRM is data-driven, so there is a fair amount of work creating all the data necessary to render a module. The Professional and Enterprise editions have a Module Builder that can help create the data, but you can certainly do it manually. There is a Module Development Guide at http://www.splendidcrm.com/Documentation/tabid/233/rvdwktid/community-edition-module-development-guide-138/Default.aspx
The best advice is to copy the code and the data for a smilar module and just rename the old to the new.