Rx stands for .NET Reactive Extensions, linked from your second link:
The Reactive Extensions (Rx)...
...is a library to compose asynchronous and event-based programs using observable collections and LINQ-style query operators.
Tx seems to be an library written on top of Reactive Extensions, which allow you to query and monitor logs:
[Query] as if all the events were in a database, except no database is involved, the query happens directly on raw logs/traces or real-time sessions
Your confusion with Java seems to come from searching the web on RXTX
, which is a serial and parallel communications library for Java, not really relevant to the subject at hand. :-)