It is possible to get free online access to UNIX or to OpenVMS; these can be useful in building up your experience on a platform when starting from scratch – or when a review is required.
One of the oldest public access systems in the country is the Super Dimension Fortress (or SDF as it is usually called). SDF offers free accounts, but does ask for US$1 to gain standard access. This isn’t because access is expensive, but because too many people have used the facilities for nefarious purposes (the process suggests that the new user is not a person who will strike and leave).
SDF runs NetBSD on DEC Alphas; this was driven mainly by security and stability. Previously, Stephen Jones, the proprietor, ran SDF using Linux on Intel for several years (which he describes as “the dark years”). BSDTalk had an interview with him back in 2006.
You could also try PolarHome – this shell provider provides access to hosts running Linux (Red Hat, Debian, SUSE, Ubuntu, or Mandriva), OpenVMS (Alpha or VAX), OpenBSD, FreeBSD, NetBSD, HPUX, IRIX, QNX, Solaris, Ultrix, AIX, Tru64, and OpenStep. Unfortunately it requires payment for shell accounts – again because of abuse. The payment is 10 units of your local currency or US$2, whichever is more – and this is per host as well. No other site provides this diverse of a selection.
For truly free UNIX shell accounts, one can try Grex, which is a more professionally-run system (Polarhome and SDF are sole proprietorships). Grex offers totally free shell accounts, but also has memberships (for people to help support the site). It is possible that Grex has the most users as well. Like the others, paid membership does have its privileges – but unlike the others, membership is mainly to provide support for Grex, rather as a security feature.
For OpenVMS, there is a very unique online shell provider: Deathrow Cluster. This is a cluster of three machines running OpenVMS 7.3 – one VAX, one Alpha, and one emulated VAX (SIMH) on a dual Xeon machine. This last is a perfect example of what can be done with an emulator, especially with SIMH which can emulate all manner of old Digital and IBM hardware. However, SIMH does not emulate the Digital Alpha, unfortunately. Like Grex, Deathrow provides completely free shell accounts; like SDF and Polarhome, it is (or appears to be) mainly one person’s purpose to keep it running with a lot of volunteer help.
Any of these will be good sources to keep your shell skills sharp – and in some cases, programming as well. They’re also good people to support; why not offer them some donations if you can?