  The JVO ALMA WebQL web service - available through the JVO ALMA FITS archive
- has been upgraded to include legacy data from other telescopes, for example
Nobeyama NRO45M in Japan. The updated server software has been renamed
FITSWebQL. In addition, a standalone desktop version supporting Linux, macOS
and Windows 10 Linux Subsystem (Bash on Windows) is also available for download
from http://jvo.nao.ac.jp/~chris/ .
  The FITSWebQL server enables viewing of even 100GB-large FITS files in a web
browser running on a PC with a limited amount of RAM. Users can interactively
zoom-in to selected areas of interest with the corresponding frequency spectrum
being calculated on the server in near real-time. The client (a browser) is a
JavaScript application built on WebSockets, HTML5, WebGL and SVG.
  There are many challenges when providing a web browser-based real-time FITS
data cube preview service over high-latency low-bandwidth network connections.
The upgraded version tries to overcome the latency issue by predicting user
mouse movements with a Kalman Filter in order to speculatively deliver the
real-time spectrum data at a point where the user is likely to be looking at.
The new version also allows one to view multiple FITS files simultaneously in
an RGB composite mode (NRO45M FUGIN only), where each dataset is assigned one
RGB channel to form a colour image. Spectra from multiple FITS cubes are shown
together too.
  The paper briefly describes main features of FITSWebQL. We also touch on some
of the recent developments, such as an experimental switch from C/C++ to Rust
(see https://www.rust-lang.org/) for improved stability, better memory
management and fearless concurrency, or attempts to display FITS data cubes in
the form of interactive on-demand video streams in a web browser.
