These are the following basic-dialects which are good:
gambas
freebasic
scriptbasic
chipmunkbasic
jabaco
maven-sb4j
ajbasic
objectivebasic
All these can also be used for making gui applications which differ with each other, database connecting tools, and in the area of webserver pages, scriptbasic and gambas-gbs3 are already there, whereas if you can get fb-curl and fb-simplewebserver and integrate them into freebasic framework, then also freebasic-server-pages.
If you are very particular with gwbasic compatibility then choose bwbasic (gwbasic enhanced for freebsd and linux), but I don't think there is much of any difference with some others.
However for graphics with bwbasic you have to contend with x11 based options or wait until it adds support for tk, fox, and other well known toolkits.
If you are willing to look for:
robust vb-like development environment + basic server pages, then choose gambas.
robust interpreter supported with a thin but good ide: freebasic, and if you can get fb-curl and fb-simplewebserver and integrate them into freebasic framework, then also freebasic-server-pages.
robust web-engine for basic server pages, then scriptbasic, and thinbasic
syntax influenced with python/perl/ruby, then scriptbasic and yabasic3
easy and very standard syntax: would be obasic (openbasic) in future, currently freebasic and scriptbasic are two varied flavors or traditional basic, whereas gambas and jabaco are a varied vb6 dialects.