ZDoom 2.8.1 has been released. This is primarily a bugfix version over version 2.8.0 with some small additions:

• #region/#endregion is now supported for text lumps. ZDoom doesn't do anything with them but ignore them, but this allows editors to treat them however they like.
• Better localizability of the menus.
• Terrain definitions can now be optional.
• Walking into an area with a reverb effect no longer mutes all sound.
• Heretic's time bomb artifacts now spawn in the proper locations.
• Heretic's powered firemace balls once again seek their targets.
• The whirlwind attack used by Heretic's Ironlich sometimes fizzled out immediately.
• Instant sector movement actions are again instant.
• Various other minor fixes.

After 2.5 years, there's finally a new release of ZDoom and a new ACC to go with it. Visit the download page to get them. There have been significant changes to ZDoom over the years, including:

Mac OS X
The OS X version of ZDoom now features a native Cocoa back end that significantly increases performance, in many case doubling frame rates, and is also more stable than the previous version.

Linux
Linux now uses SDL2 which can produce less frame jitter with high frame rates, has some vsync support, and fullscreen is now a "desktop fullscreen" mode.

Windows
ZDoom already worked great on Windows, so nothing has changed here.

Everything else
A fairly complete list of changes since 2.7.1 is available on the wiki. I'll probably pick out some highlights to list here eventually. Maybe. Or just read the comments for this post, since other people already did it.

ZDBSP has been updated to version 1.19. This version fixes a minor bug that could prevent it from loading certain UDMF maps.

ZDoom 2.7.1 is now available from the download page. This version includes the following changes from 2.7.0:

• Added new additive GameInfo keywords: AddCreditPage, AddPlayerClasses, and AddInfoPage.
• Added a new DONTDRAIN flag to mark actors as ineligible for vampirism attacks.
• Compatibility fixes for Ultimate Simplicity map07, Cheogsh map01, Super Sonic Doom map31
• Polyobject mirror numbers can no longer be changed with SetLineSpecial. This was never a supported feature and caused problems for legitimate uses of SetLineSpecial on polyobject lines.
• The powered-up Gold Wand was not puffing on actors.
• Disabled Heretic's punishment cheats when in allcheats mode.
• Objects that explode on death no longer deal the damage they were dealt instead of their own.
• Vampirism attacks now respect damage reduction.
• Demo recording now writes correct user info to demos.
• ACS's PlaySound for looping sounds now works properly when using channel flags.

For those interested in ZDoom's development, the source code repository has migrated to GitHub: http://github.com/rheit/zdoom

To use the new ACS features of ZDoom 2.7, ACC 1.54 is also available now.

It's been almost a year since the last release, so here's ZDoom 2.7.0. In addition to various bug fixes, here are some highlights of the new features:

• Added support for Doom 3: BFG Edition's modified IWADs, including No Rest for the Living.
• ACS:
  • Made dynamic strings persistent. ACS can now safely generate up to one million new strings.
  • Added new functions: Sqrt, FixedSqrt, VectorLength, CheckFont, GetCVarString, GetUserCVar, GetUserCVarString, IsTIDUsed, LineAttack, SetCVar, SetCVarString, SetUserCVar, SetUserCVarString, SpawnDecal, and UniqueTID.
  • Added HUD layers, visibility flags, additive blending, and alpha parameter to HudMessage and HudMessageBold.
  • Also added HUD message wrapping and clipping with SetHudClipRect and SetHudWrapWidth.
  • Added acsprofile console command.
  • Added PLAYERINFO_FOV and _DESIREDFOV to GetPlayerInfo.
  • Added support for desaturated translations.
  • Added the ability to retrieve the ReactionTime, Height and Radius properties through GetActorProperty.
  • Added CHANGELEVEL_PRERAISEWEAPON to ChangeLevel.
• DECORATE:
  • FLOATBOB things are no longer moved physically when bobbing.
  • Added Player.FallingScreemSpeed, Player.GruntSpeed, MinSelectionAmmo1, and Weapon.MinSelectionAmmo2.
  • Added random state duration and A_SetTics.
  • A_Explode's ''affectsource'' parameter has been turned into a flag. Plus, added NOTMISSILE flag to A_Explode as well as to A_RadiusThrust.
  • A_RadiusThrust can use negative ''force'' values.
  • Added A_JumpIfTargetInsideMeleeRange, A_JumpIfTargetOutsideMeleeRange, A_SetDamageType, and A_CheckLOF.
  • Added INVENTORY.NEVERRESPAWN, INVENTORY.NOSCREENFLASH, POWERSPEED.NOTRAIL, and PLAYERPAWN.CROUCHABLEMORPH.
  • Added JLOSF_NOAUTOAIM flag to A_JumpIfTargetInLOS.
  • Added WRF_DISABLESWITCH to A_WeaponReady.
  • A_Light can use negative values to darken the scene.
  • Added NORANDOMPUFFZ flag to A_CustomPunch, A_FireBullets, and A_CustomBulletAttack.
  • Added SXF_USEBLOODCOLOR, SXF_CLEARCALLERTID, SXF_MULTIPLYSPEED, SXF_TRANSFERSCALE, SXF_TRANSFERSPECIAL, and SXF_CLEARCALLERSPECIAL flags to A_SpawnItemEx.
  • Added the ability to adjust the vertical offset of a rail attack to A_RailAttack and A_CustomRailgun.
  • Player-fired seeker missiles' range at which the missiles initially lock-on a tracer can be set via MaxTargetRange actor property.
  • ReactionTime added to DECORATE expressions.
  • Added NoDelay state flag.
  • Added Bounce actor states.
  • Fixed few cases of DECORATE definitions inaccuracies for Doom, Heretic, Hexen and Strife actors.
• Added the ability to define mod-specific console variables through the addition of the CVARINFO lump.
• Added Floor_RaiseAndCrushDoom.
• FONTDEFS: Backported SPACEWIDTH from ECWolf.
• LANGUAGE: Brazilian Portuguese support.
• MAPINFO: Added ForgetState, RememberState, and SpawnWithWeaponRaised flags for map definitions and NoRandomPlayerclass for GameInfo definitions.
• FluidSynth now recognize libfluidsynth.dll as a valid alias for fluidsynth.dll. Some FluidSynth defaults have also been tweaked.
• OPL emulation now includes two new OPL3 emulators, and you can have the equivalent of up to eight chips for one song. In addition, all OPL emulations support full stereo panning (something the real hardware cannot do).
• Updated foo_DUMB.
• Implemented additive rendering for 3D floors.
• Added Quake-like no-clipping with noclip2.
• Exported the scoreboard text to LANGUAGE.
• The sound system should now precache nearly all sounds used by actor properties and ambient sounds, and the MAPINFO command "PrecacheSounds" can be used to precache other sounds.
• Arbitrary FPS cap with vid_maxfps.
• Increased maximum resolution to 5760×3600.
• Added lightfog property for sidedefs.
• Added ability in UDMF to specify things to spawn by thing specials and Hexen breakable items by names with arg1str, as well as the ability to set initial values to a thing's user variables.
• Added new node format for complex UDMF maps which need fractional precision on node splitters.
• The alternate HUD now features a Berserk indicator and a customizable time display.
• Weapon slots can be configured from the Customize controls menu.
• RandomSpawners now respect -nomonsters.

ZDBSP has received a small bug fix and is now at version 1.18.1. This corrects a problem in earlier versions that could potentially create invalid nodes with maps that have more than 65535 lines or with maps that use the new node format introduced in ZDBSP 1.18.

ZDBSP 1.18 is now available. This version introduces a new node format for better compatibility with UDMF maps that have vertices with fractional coordinates.

ACC 1.53 is now available and supports the latest features of ZDoom 2.6, such as scripts with four parameters, waiting on named scripts, and some very minor bug fixes.

In addition, the -h command line option no longer silently promotes non-Hexen features to the ZDoom script format. You now get an error when you try to use ZDoom-features in Hexen-compatible mode.

I would have put this up with ZDoom 2.6.0, but it slipped my mind. Sorry about that.