These are the following basic-dialects which are good:
gambas
jabaco
objectivebasic
freebasic
chipmunkbasic
These are the following embeddable basic-dialects which are good
scriptbasic
maven-sb4j
ajbasic
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 they are not there then you may have to download and copy-paste the library and header files under the lib and include directory of freebasic respectively)
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 or jabaco with maven-sb4j.
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.
So, these are all robust and may become usable at least after adding some few modules.
Borrowed some minor features from python/perl/ruby: scriptbasic (and also 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.