Gypsy Makes a great point.
The MT, 2300 and MGT task systems work well with CT, MT, 2300, and MGT characters.
TNE and T4 task systems can be swapped easily enough for TNE and T4 characters.
T20 characters and tasks are different enough as to be not easily swapped.
Some other task systems that could be imported easily as the skill and attribute levels are similar to CT/MT/MGT:
Burning Wheel: Add Attribute/3 as base for level 0, adding 1d per skill level. double base ob for unskilled. Simple= Ob1, Routine Ob2, Diff Ob 4 , Form ob7 Imp Ob11. Need to add beliefs and artha to make it work well, or simply allow all rolls to open end. (Note: This gives a base of 3d for level 1 skill in an average stat, and 4d in a 9+ stat.. add forks, and you can get 2 more dice, and an advantage for another die... meaning typical people roll 5-8 dice... without artha)
CORPS: Att/3 + skill level as CORPS-equivalent level. TN Sim=2, Rou=5, Dif=8, Form=11, Imp=14
EABA: Convert attribute to dice using the levels to dice conversions as normal. Each level of skill to level 5 is a +1D to skill. TN Sim=3, Rou=7, Dif=11, Form=15, Imp=19
ooWOD: Skill level + (Att/3) dice vs Simple =TN2, Routine TN4, Difficult TN6, Formidible TN8, Impossible TN10
oWOD: Skill level + (Att/3) dice vs 7+; Simple 1s, Routine 2s, Diff 3s, Form 5s, Imp 7s
T&C can be migrated rather easily; there are several sets: Bk2, Bk7, MT/TNE/T4 (expanded Bk7), T20 (Expanded Bk2), MGT. GTFT is less easily used, but is useable; be warned, the GT credit is not the OTU credit, so prices may not always match.
MT, MGT, and TNE combat systems are almost purely task based, and quite portable to other editions; T4, while task based, is slightly more tied to its task mechanics, but is also portable as a module.
Ship design and ship combat intertwine heavily.
Bk2 can handle Bk2 and MGT
Bk5 can handle Bk5, MT, and T20 designs easily; CT and MGT designs with a little work.
MT's HG can handle MT, Bk5, and T20 designs easily. Bk2 and MGT designs with little effort, namely the same conversions needed for Bk5...
T20 can handle MT, Bk5, and T20 designs; non-T20 designs need some numbers crunched to finish out the needed data. CT and MGT designs need conversion to Bk5/MT plus the addition of structure points...
TNE and T4 use the same design engine, and have incompatible combat data, but the designs can be rerated; in both cases, due to the detail levels, other design systems do not convert well; MT converts with the least fuss.
MT's vehicular combat system (which is allowed to be used with ships) can handle designs from all editions if you have the spreadsheet to hand to generate the Hits data from tonnages, and are using stock weapons only. (I treat 3-ton TNE/T4 turrets as +1 UCP over comparable 1-ton turrets.)
World design differs only slightly from edition to edition; T20 and MGT have the most divergence. MT's Hard Times and TNE both have collapse procedures to downrate standard UWP's to reflect the settings. GT has a wholly different world system, but the results are similar; UWP conversions to GURPS stats are somewhere in GT (I think in GT and/or BTC)
Cybernetics: TNE and MGT cyber are not per se compatible, but either is relatively portabe to other systems.
