Answering from a strictly amateur radio perspective.
No doubt someone may have collected and collated a list of some specific typical frequencies, but for amateur radio fixed frequencies for "services" isn't really a thing. So such a list will not be very useful. There are conventions, such as a historically specific frequency for nets and so on, but technically all amateurs have access to all frequencies their privileges allow, and we negotiate for that part of the spectrum each time we decide to transmit. The nets "have" those frequencies only because good operating practices means if you stumble onto a net you would realize that asking the net to move isn't very feasible when you can just move your own traffic up or down. But no net owns any frequency.
Further, most rules about operating globally require an operator to be at the station when transmitting. There are exceptions to this, but by and large you are not going to find unattended transmissions unless those are associated with a club or other convention (you mention APRS, for which the retransmitting of aggregate traffic by repeaters is merely a convention, and one exception that proves the rule). The upshot is the great majority of operators will have to be at "the control point" at all times, even for APRS in their cars or whatever.
Most countries have rules about the content of amateur radio transmissions, which may vary from region to region but are guided by the proviso that the content be more or less trivial and unrelated to most subjects other than the hobby itself. Thus, most beacon traffic, when allowed, will be about weather, trivial updates to statuses, and location or propagation information. The regulations are very clear that the amateur service should not engage in what could be broadly characterized as "broadcast" activity.
And one thing is for sure: it is strictly contrary to any amateur radio license to enage in any on-air activities that require or request payment of any kind. Thus, any "service" has to be 100% volunteer data provided or repeated for free. This is in addition to any requirements about the content. So, as you can see, what sorts of "services" amateurs can offer are more or less only of interest to other amateurs.
How to Find Data Transmissions of Interest
So what you will have to do is find someone transmitting in a mode of interest to you, probably by consulting your local bandplan(s), or researching that mode to see if there are global agreements in place about how they are to be coordinated (e.g., APRS, again). You won't generally find any "digicasts" of any kind in the parts of the amateur bands dedicated to voice operations, for example, though this is enforced by convention in most cases. Most operators on these modes will use computer software to show a large bandwidth in a waterfall display to see if there is traffic of interest in the usual places, and then tune, listen, retransmit (if legal), or respond as appropriate.
This same technique can be used to see if there is interesting traffic outside of the amateur bands, and there may be some list of those out there. But for amateur transmissions it is about convention, habit, and technique.
If you find traffic of interest in the amateur bands, at least if that traffic is compliant with international amateur radio agreements, it cannot be encrypted. At least the scheme and traffic should never be encrypted such that the traffic is "secret" or obscured. Again, there are grey areas, but the regulations are broadly very clear about this, and all operators know (or ought to know) that the small amount of spectrum we have exclusive access to is ours only provisionally.