* Fixed performance regression in messaging ([GAUDI-1319](https://its.cern.ch/jira/projects/GAUDI/issues/GAUDI-1319), [mr !427](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/427))
* Fixed issue with mulltiple runs of *thistwrite* test ([GAUDI-1316](https://its.cern.ch/jira/projects/GAUDI/issues/GAUDI-1316), [mr !427](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/427))
* Fixed various printouts ([mr !438](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/438))
* Added `Gaudi::tagged_bool` class ([mr !440](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/440))
* Fixed compilation error in overload resolution of `TupleObj::farray` for gcc7 ([mr !446](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/446))
* Added missing header guard to `GaudiKernel/invoke.h` ([mr !459](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/459))
* Improved behaviour of `get_host_binary_tag.py` for unknown distribution detection fails (mr [!471](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/471))
* Add support for CTest stdout compression in XML reports (mr [!453](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/453))
* Remove `IssueSeverity` support from `StatusCode` (mr [!477](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/477))
* Remove include of deprecated `GaudiKernel/AlgFactory.h` header (mr [!414](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/414))
* Bugfixes
* Fix abnormal termination caused by use of an invalid context when AlgExecStateSvc is verbose (mrs [!475](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/475))
* Fix unnamed lock in example code (mr [!487](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/487))
* Fixed handling of data dependencies in `ToolHandles` (mr [!429](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/429), [!501](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/501))
* Fixed use of messages in `ApplicationMgr::i_startup` (mr [!436](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/436))
* Improvements
* Add compile-time warning about ignoring returned `StatusCode` (mr [!386](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/386))
* Reverse the order in which `IoComponentMgr` io_finalizes components (mr [!469](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/469))
* Added protection on event slot creation in `HiveWhiteBoard` (mr [!502](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/502))
* Made `PrecedenceSvc` recognize data loader algorithm (mr [!473](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/473), [!506](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/506))
* Improvements to temporal and topological execution flow tracer [!444](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/444)
* Optimized `AvalancheScheduler` by avoiding the use of algo names and prefering algo indexes (mr [!482](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/482))
* Replaced all `std::bind` by lambdas in `AvalancheScheduler` (mr [!481](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/481))
* Fixed race condition in `AvalancheScheduler` (mr [!479](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/479))
* Dropped unused member `m_updateNeeded` in `AvalancheScheduler` (mr [!478](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/478))
* Simplified (aka optimized) usage of ttb tasks in `AvalancheScheduler` (mr [!452](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/452))
* Add `DecisionNode` negation/inversion to `AvalancheScheduler` (mr [!434](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/434))
* Migrate GaudiHive tests to QMT format (mr [!419](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/419))
* Fixes for CI tests (mr [!503](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/503))
* Fixed handling of data dependencies in `ToolHandles` (mr [!429](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/429), [!501](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/501))
* Made `PrecedenceSvc` recognize data loader algorithm (mr [!473](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/473), [!506](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/506))
* Added test for the `TimelineSvc` (mr [!415](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/415))
* Add support for CTest stdout compression in XML reports (mr [!453](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/453))
* Made multi_input tests more reliable (mr [!468](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests/468))
The full list of changes can be found on [Gitlab](https://gitlab.cern.ch/gaudi/Gaudi/merge_requests?milestone_title=v30r0&scope=all&state=merged).