Yabasic
Yabasic (Yet Another BASIC) is a free and open source BASIC interpreter for Windows and Unix platforms. Yabasic was originally developed by Marc-Oliver Ihm, who released the last stable version 2.763 in 2005. As a continuation of the project, version 3 is now developed by a team centered around Pedro Sá and Thomas Larsen. The Yabasic interpreter is quite compact at about 250 kilobytes total.