There is no way currently, OS does not allow to install new apps.

How can I use additional web application such like web-office in SoongyOS ?

I don't know what is webOS, but I like Soongy, because uploading of files is very simple here.

I think would be better to add more info in site regarding WebOS and also why Soongy system is better then other systems

Yes Soongy may be called WebOS, but it is more some easy and simple file uploading and view system and btw only pictures are working well now