I wanted to point out two general purpose OOT modules we developed for some internal work and recently published: gr-pdu_utils and gr-timing_utils, available here:
These contain a variety of useful blocks for manipulating PDUs, converting to/from PDUs/streams, and an assortment of functions we've needed over time. A lightweight method for reasonable (+/- a few samples) timing of receive bursts is included based on UHD-style rx_time tags, and UHD-style transmit timing is supported as well for transceiver applications. The PDU Utils module has a fairly good README describing use, Timing Utils README is coming soon (the module was published early as a the two are related).
These modules were initially developed for bursty transceiver applications, but have found use in tons of other ways over the past few years from vector signal measurements to static data analysis to FHSS systems, and sometimes it's just more useful to work with messages vs streams.
There are other ways to do some of what we have implemented here, but these modules were developed to address some features we needed in a lightweight, easy to use way. We have used the core blocks fairly extensively, and they should work very well, though I can't promise there aren't edge cases we haven't worked through yet, and there are some in-progress blocks. Bug reports/fixes are appreciated - hope some of you find these modules useful.
Jacob