Most of the open source software around expose its code over some HTTP service. I would like to open and browse such code from Emacs, but AFAICS tramp only allows for ssh<
There are two or three html viewers for emacs; I'd use emacs-w3m. If you want to edit something remote via HTTP(S), perhaps Tramp's dav external method will work for you.
M-x browse-url-emacs
RET http...
RET
You might need to use M-x normal-mode
RET afterwards to set the appropriate mode for the buffer.